Have you tried re-copying the game from the disk image? Perhaps you should go to ~/Library/Preferences (or maybe Application Support/Frictional Games/ and delete the Penumbra folder(s). This will remove all the saves but also remove all the settings and combined with copying from the disk image result in a fresh install.
You might also want to open the Disk Utility and run a verify disk permissions on the harddrive.
I think there is a problem with writing a file and that is why you get the problem. The game tries to write a file, it should not have to though, that contains navigation data for the enemy but this fails for some reason. Since the enemy then does not have any way of navigating it gets stuck and that is also probably why the music get stuck.
Open the Terminal (in Applications/Utilities) and type:
touch /Applications/Penumbra\ Collection/Black\ Plague/maps/*.node
then hit enter and you can close the Terminal.
Then try running the game from start and see if that helps. The above "touches" all the enemy navigation files, which changes their modify date, which I hope will make the game think that the files are new enough and not try and re-create them.
If it's possible I could just exchange this copy for a PC one, but I'm not sure if that's ok to do. I just think that's probably the easiest/fastest way to solve this problem since my PC is a much better computer for gaming (to be honest I don't know why I didn't download it to that computer in the first place :|) but again, I'm not sure if I'm aloud to do that.
Thanks! I'm definitely gonna try that out tomorrow, hopefully that solves the problem. If it doesn't, well... Crys playthroughs are always fun to watch.
so sorry it took me so long to reply, but i forgot i was going on vacation when i said i'd try the PC conversion thing the next day so that pretty much explains the delayed response anyways, running it on windows seems to have done the trick because both of the problems are fixed. thanks guys! great game so far btw