It isn't the stages becauese i dn't have any custom stages loaded... and can you tell me what SC_selmap.pac and Common5.pac are?
The file, sc_selmap.pac, is used for the stage select screen. It's responsible for the stage select icons and names. It's also part of common5.pac.
Again, if you modified anything on that file, make sure that it isn't corrupted, and that it uses less memory than normal.