O.K. now I really fixed it. I have been playing with the ring tones and the voice notes for three days with no problems and no "Device Media Processor is Busy" notice.
This is how I did it on a Verizon Blackberry 8830 upgraded to OS18.104.22.168
First I did a backup using the Desktop Manager. Then I did a "Wipe" (go to Options> Security Options> General Settings, press the Menu key and select "Wipe Handheld".
Then, using the Desktop Manager, I did a "Selective Restore" by choosing Backup & Restore then Advanced, and then selecting only the following items from the list on the left side (my backup file): Address Book, Calendar, Map Locations, Password Keeper and Browser Bookmarks. That's it! Don't forget to turn the connection back on.
all this was done under the close phone supervision by a very helpful fellow from Blackberry. You know who you are. Thank you.