Error opening processing. was using 3 and tried to install 2. now none of them open.

SRI

GoToLoop

P3 & P2 3rd-party libraries are very incompatible in general.
Therefore we have to specify unique "Sketchbook locations" for both.

In P2, hit CTRL + Comma to go to "Preferences...".
Then change its "Sketchbook location:" folder path to be diff. than P3's.

SRI

P3 runs now but P2 doesnt open. :/

GoToLoop

1. Open P3 and hit CTRL+Comma.
2. Then click at the last bottom option which opens the folder where "preferences.txt" file is.
3. Now close Processing's IDE so you can edit "preferences.txt" file safely.
4. Within "preferences.txt" search for "sketchbook.path=".
5. Type in some path folder diff. from the 1 specified at "sketchbook.path.three=".
6. Save it and hopefully you can use P2 (even P1) after that modification. [-O<

Attention: We can't have diff. versions of Processing IDEs (PDE) open at the same time. Except P1. :-\"