precisions would be appreciated too…
maybe the type of strings you want to save ? the savestrings instructions ?………

This is unreadable.
You have textual data, copy it and paste it.

Reminder: Programming Questions section is for questions about code you show; here, you just show some stack trace, without any code nor context. As Pauline said, we lack information to help you.

got the same error when saving code example P_1_1_1_01 from "the nature of code" using P2.0b6 on Win7-64bit:

1. java.lang.NumberFormatException: For input string: "2.0.0+"
2.     at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
3.     at java.lang.Integer.parseInt(Integer.java:458)
4.     at java.lang.Integer.parseInt(Integer.java:499)
5.     at processing.app.contrib.InstalledContribution.<init>(InstalledContribution.java:75)
6.     at processing.app.Library.<init>(Library.java:88)
7.     at processing.app.Library.<init>(Library.java:83)
8.     at processing.app.Library.list(Library.java:470)
9.     at processing.app.Library.list(Library.java:461)
10.     at processing.app.Mode.rebuildLibraryList(Mode.java:174)
11.     at processing.app.Mode.rebuildImportMenu(Mode.java:312)
12.     at processing.app.Base.rebuildSketchbookMenus(Base.java:1204)
13.     at processing.app.Sketch.updateInternal(Sketch.java:906)
14.     at processing.app.Sketch.saveAs(Sketch.java:869)
15.     at processing.app.Editor.handleSaveAs(Editor.java:2137)
16.     at processing.mode.java.JavaEditor.handleSaveAs(JavaEditor.java:534)
17.     at processing.app.Editor$12.actionPerformed(Editor.java:610)
18.     at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
19.     at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
20.     at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
21.     at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
22.     at javax.swing.AbstractButton.doClick(AbstractButton.java:357)
23.     at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:809)
24.     at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:850)
25.     at java.awt.Component.processMouseEvent(Component.java:6290)
26.     at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
27.     at java.awt.Component.processEvent(Component.java:6055)
28.     at java.awt.Container.processEvent(Container.java:2039)
29.     at java.awt.Component.dispatchEventImpl(Component.java:4653)
30.     at java.awt.Container.dispatchEventImpl(Container.java:2097)
31.     at java.awt.Component.dispatchEvent(Component.java:4481)
32.     at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4575)
33.     at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4236)
34.     at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4166)
35.     at java.awt.Container.dispatchEventImpl(Container.java:2083)
36.     at java.awt.Component.dispatchEvent(Component.java:4481)
37.     at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:648)
38.     at java.awt.EventQueue.access$000(EventQueue.java:84)
39.     at java.awt.EventQueue$1.run(EventQueue.java:607)
40.     at java.awt.EventQueue$1.run(EventQueue.java:605)
41.     at java.security.AccessController.doPrivileged(Native Method)
42.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
43.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
44.     at java.awt.EventQueue$2.run(EventQueue.java:621)
45.     at java.awt.EventQueue$2.run(EventQueue.java:619)
46.     at java.security.AccessController.doPrivileged(Native Method)
47.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
48.     at java.awt.EventQueue.dispatchEvent(EventQueue.java:618)
49.     at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
50.     at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
51.     at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
52.     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
53.     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
54.     at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
55. java.lang.NumberFormatException: For input string: "2.0.0+"
56.     at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
57.     at java.lang.Integer.parseInt(Integer.java:458)
58.     at java.lang.Integer.parseInt(Integer.java:499)
59.     at processing.app.contrib.InstalledContribution.<init>(InstalledContribution.java:75)
60.     at processing.app.Library.<init>(Library.java:88)
61.     at processing.app.Library.<init>(Library.java:83)
62.     at processing.app.Library.list(Library.java:470)
63.     at processing.app.Library.list(Library.java:461)
64.     at processing.app.Mode.rebuildLibraryList(Mode.java:174)
65.     at processing.app.Mode.rebuildImportMenu(Mode.java:312)
66.     at processing.app.Base.rebuildSketchbookMenus(Base.java:1204)
67.     at processing.app.Sketch.updateInternal(Sketch.java:906)
68.     at processing.app.Sketch.saveAs(Sketch.java:869)
69.     at processing.app.Editor.handleSaveAs(Editor.java:2137)
70.     at processing.mode.java.JavaEditor.handleSaveAs(JavaEditor.java:534)
71.     at processing.app.Editor$12.actionPerformed(Editor.java:610)
72.     at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
73.     at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
74.     at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
75.     at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
76.     at javax.swing.AbstractButton.doClick(AbstractButton.java:357)
77.     at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:809)
78.     at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:850)
79.     at java.awt.Component.processMouseEvent(Component.java:6290)
80.     at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
81.     at java.awt.Component.processEvent(Component.java:6055)
82.     at java.awt.Container.processEvent(Container.java:2039)
83.     at java.awt.Component.dispatchEventImpl(Component.java:4653)
84.     at java.awt.Container.dispatchEventImpl(Container.java:2097)
85.     at java.awt.Component.dispatchEvent(Component.java:4481)
86.     at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4575)
87.     at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4236)
88.     at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4166)
89.     at java.awt.Container.dispatchEventImpl(Container.java:2083)
90.     at java.awt.Component.dispatchEvent(Component.java:4481)
91.     at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:648)
92.     at java.awt.EventQueue.access$000(EventQueue.java:84)
93.     at java.awt.EventQueue$1.run(EventQueue.java:607)
94.     at java.awt.EventQueue$1.run(EventQueue.java:605)
95.     at java.security.AccessController.doPrivileged(Native Method)
96.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
97.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
98.     at java.awt.EventQueue$2.run(EventQueue.java:621)
99.     at java.awt.EventQueue$2.run(EventQueue.java:619)
100.     at java.security.AccessController.doPrivileged(Native Method)
101.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
102.     at java.awt.EventQueue.dispatchEvent(EventQueue.java:618)
103.     at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
104.     at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
105.     at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
106.     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
107.     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
108.     at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
109. java.lang.NumberFormatException: For input string: "2.0.0+"
110.     at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
111.     at java.lang.Integer.parseInt(Integer.java:458)
112.     at java.lang.Integer.parseInt(Integer.java:499)
113.     at processing.app.contrib.InstalledContribution.<init>(InstalledContribution.java:75)
114.     at processing.app.Library.<init>(Library.java:88)
115.     at processing.app.Library.<init>(Library.java:83)
116.     at processing.app.Library.list(Library.java:470)
117.     at processing.app.Library.list(Library.java:461)
118.     at processing.app.Mode.rebuildLibraryList(Mode.java:174)
119.     at processing.app.Mode.rebuildImportMenu(Mode.java:312)
120.     at processing.app.Base.rebuildSketchbookMenus(Base.java:1204)
121.     at processing.app.Sketch.updateInternal(Sketch.java:906)
122.     at processing.app.Sketch.saveAs(Sketch.java:869)
123.     at processing.app.Editor.handleSaveAs(Editor.java:2137)
124.     at processing.mode.java.JavaEditor.handleSaveAs(JavaEditor.java:534)
125.     at processing.app.Editor$12.actionPerformed(Editor.java:610)
126.     at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
127.     at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
128.     at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
129.     at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
130.     at javax.swing.AbstractButton.doClick(AbstractButton.java:357)
131.     at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:809)
132.     at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:850)
133.     at java.awt.Component.processMouseEvent(Component.java:6290)
134.     at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
135.     at java.awt.Component.processEvent(Component.java:6055)
136.     at java.awt.Container.processEvent(Container.java:2039)
137.     at java.awt.Component.dispatchEventImpl(Component.java:4653)
138.     at java.awt.Container.dispatchEventImpl(Container.java:2097)
139.     at java.awt.Component.dispatchEvent(Component.java:4481)
140.     at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4575)
141.     at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4236)
142.     at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4166)
143.     at java.awt.Container.dispatchEventImpl(Container.java:2083)
144.     at java.awt.Component.dispatchEvent(Component.java:4481)
145.     at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:648)
146.     at java.awt.EventQueue.access$000(EventQueue.java:84)
147.     at java.awt.EventQueue$1.run(EventQueue.java:607)
148.     at java.awt.EventQueue$1.run(EventQueue.java:605)
149.     at java.security.AccessController.doPrivileged(Native Method)
150.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
151.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
152.     at java.awt.EventQueue$2.run(EventQueue.java:621)
153.     at java.awt.EventQueue$2.run(EventQueue.java:619)
154.     at java.security.AccessController.doPrivileged(Native Method)
155.     at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
156.     at java.awt.EventQueue.dispatchEvent(EventQueue.java:618)
157.     at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
158.     at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
159.     at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
160.     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
161.     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
162.     at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

code:

1. // P_1_1_1_01.pde
2. //
3. // Generative Gestaltung, ISBN: 978-3-87439-759-9
4. // First Edition, Hermann Schmidt, Mainz, 2009
5. // Hartmut Bohnacker, Benedikt Gross, Julia Laub, Claudius Lazzeroni
6. // Copyright 2009 Hartmut Bohnacker, Benedikt Gross, Julia Laub, Claudius Lazzeroni
7. //
8. // http://www.generative-gestaltung.de
9. //
10. // Licensed under the Apache License, Version 2.0 (the "License");
11. // you may not use this file except in compliance with the License.
12. // You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
13. // Unless required by applicable law or agreed to in writing, software
14. // distributed under the License is distributed on an "AS IS" BASIS,
15. // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16. // See the License for the specific language governing permissions and
17. // limitations under the License.
18. /**
19.  * draw the color spectrum by moving the mouse
20.  *      
21.  * MOUSE
22.  * position x/y        : resolution
23.  *
24.  * KEYS
25.  * s                   : save png
26.  * p                   : save pdf
27.  */
28. import processing.pdf.*;
29. boolean savePDF = false;
30. int stepX;
31. int stepY;
32. void setup(){
33.   size(800, 400);
34.   background(0);
35. }
36. void draw(){
37.   if (savePDF) beginRecord(PDF, timestamp()+".pdf");
38.   noStroke();
39.   colorMode(HSB, width, height, 100);
40.   stepX = mouseX+1;
41.   stepY = mouseY+1;
42.   for (int gridY=0; gridY<height; gridY+=stepY){
43.     for (int gridX=0; gridX<width; gridX+=stepX){
44.       fill(gridX, height-gridY, 100);
45.       rect(gridX, gridY, stepX, stepY);
46.     }
47.   }
48.  
49.   fill(0);
50.   text("step x: " + stepX, 10,height-30);
51.   text("step y: " + stepY, 10,height-20);
52.   text("mouse x: " + mouseX, 10, height-10);
53.   text("mouse y: " + mouseY, 10, height);
54.  
55.   if (savePDF) {
56.     savePDF = false;
57.     endRecord();
58.   }
59. }
60. void keyPressed() {
61.   if (key=='s' || key=='S') saveFrame(timestamp()+"_##.png");
62.   if (key=='p' || key=='P') savePDF = true;
63. }
64. // timestamp
65. String timestamp() {
66.   Calendar now = Calendar.getInstance();
67.   return String.format("%1$ty%1$tm%1$td_%1$tH%1$tM%1$tS", now);
68. }

works fine for me, adding  import java.util.Calendar;
processing 2.08
mac 0S

Looks like Processing internals try to parse the version number ("2.0.0+") which is curiously formatted.
Although when I look into the lib/version.txt file in the Processing distribution, I read 2.0b8, which isn't a real number either.
Perhaps try 2.0b8.

thanks both! so far it doesn't affect the function of the code, it's just a bit annoying to see it ...