I Have a similar problem and restart doesnt help.
I thought it may be because i used fexplorer Ext205 to re associate mp3 files to open with windows player instead of the samsung touch player..( I read somewhere about a "memorycard full" issue with the touch player, and had the same problem) So now my mp3's open ok with windows player, but when i set a ringtone
it tells me I have Corrupted files. (But they work fine when I play them with windows player).
Wont let me assign an mp3 ringtone.
I un-installed the File explorer extension hoping to reset all file associations, To no avail.
Its frustrating me.
Is hard reset perhaps the only option, (Haven't had to Hard reset, yet). Or is there another way.? :