I've encountered this a lot time ago. Well, when I create a JJ2 level, there are several values for Ambient Soud which do not work. The values are 53, 65, 110, and 111. When I go to test the level, the first two tell me "Out of Memory", the third says that "Fatal Error in fileRead on file "Anims.j2a", error: Input past end of file" and the last says "The Animation library file "Anims.j2a" is incomplete, corrupt or of an unknown version".
Is there something wrong with the JCS, the Anims.j2a, or the JJ2 itself?

And another question: What is this 1.20 -> 1.23 Patch for? I mean, everywhere they just say you should get it, but I just can't find what it really does.

Basically, 1.20-1.23 combines 1.20-1.21, 1.21-1.22 and 1.22-1.23, all of which were patches intended to fix bugs or add features to JJ2. Most noticeably that I can think of right now, rabbits will not leave corpses in multiplayer, and you will be able to join games hosted in 1.23.

Originally Posted by UltimateSephiroth

Is there something wrong with the JCS, the Anims.j2a, or the JJ2 itself?

I would assume the errors are related to JJ2 loading sprites as well as the ambient sound. This wasn't intentional, but the sprites loaded from ambient sounds can be used to correct MCE's. Pyromanus compiled this list on ambient sounds a while ago which includes what causes errors and what sprites get loaded for both 1.23 and TSF.