Just a bit of speculation.
Say you want to send your friend some songs from your PSP to theirs. Using File Assistant v0.01, rename an mp3 to songname.jpg or some other extension. Then using FA, move it to the PHOTO folder. This would most likely be an unviewable file now. Then try and use the send feature to transfer it. Have them undo your changes with FA using their own PSP(rename it to songname.mp3 and move it to music). The only problem that could occur is the inability to send the file.