Are you using any codes like the stage roster expansion one by Phantom Wings?

Whatever file your SSS replacement is in, it's probably over the file size limit.  See this great guide here:
http://forums.kc-mm.com/index.php?topic=9293.0

For certain texture hacks, there's an extra FitMotionEtc with the texture that changes the animations of the character.  The only problem for me is that it changes the animations for EVERY texture of the character.  Is there anyway to take the animations out of FitMotionEtc with BrawlBox and only apply them to the particular.pac or.pcs of that character?  Like with the pikachu to mew hack-I want to give mew the proper animations, but I if I just put FitMotionEtc in the folder, the regular pikachu moves weird.