Motorola

I've created several ringtones on my pc and saved them to nmy ROKR, and even set them as ringtones, my problem is, it won't do it any more. when i try to copy or move from the momory card to the phone, it just exits to the multimedia main menu. i can't delete the old ones either. i can however send ringtones via bluetooth to another phone, and they work just fine. if i try and send it back to me, a "file corrupt" message comes up. pls help!!