It isn't super clear, indeed, but I think it refers to the 14 lines <property name="..."/> at the start of the file.
And, well, have you a  /home/algo/Documents/Processing/libraries folder?
Note: you must also edit build.properties

hi, if you can see a build.properties file next to the build.xml file, only make changes to that build.properties file. here, making changes to the build.xml file are not required. please read the instructions inside the build.properties file when making changes to any properties.

Thanks for your answer !

@phi.lho :
Yeah you're right I think it's better to edit the build.properties file, but I don't knowvery welle the way to do that.
I don't have the same displaying of my build.properties file than in the HowTo page andreas give me ...
Of course I don't have the folder which appears in my error and that why I want to know how to change this in the build file or in the buid.properties file.

@andreas :
I'm Linux user and it's my first try to build a library... not exactly built but re-built, because I have only change a class into the Ketai library for processing.android...
As I say to phi.lho my build.properties doesn't look like in the HowTo. Mine is more like check button.

But anyway, I have re-built the lib in another way, allways with eclipse, but more in a "run as" style, and add my classes builded to a jar file...
It's working too (prettymuch because there error into java file)

Thank you for your interest.

hi, the following is take from the howTo page, to display the properties files as text do the following:

Oh nice
Thanks a lot !