Can someone tell me why the following does not work?

I extracted the Sounds.bsa file using BSA Commander.

i replaced the two Mudcrab death .wav files with two other .wav files that are roughly the same size (in kb) and gave the two new files the names of the originals (I want a different sound to play when a mudcrab dies).

And now, the game crashes whenever I get near a mudcrab. Is replacing a sound file more complicated than I think?

edit: also, when I try adding a new Music Track, I get an "invalid directory" error when I try to choose a file. Help?

I probably am wrong, but did you do some kind of archive invalidation?
also, read lojack's thread on bsa.

Now, the Creation Kit is just being buggy. It crashes whenever I try to save - even if I just loaded the data and haven't changed anything.

edit- I figured it out from another thread... There is a bug in the Creation Kit where if you try to create a new sound object, the filepath to the .wav you choose disappears when you try to use the mod. That's why it was crashing - I opened up my plug-in again, with the missing filepath, and tried to save it.

did it work?