Rebuild the itunes Library
I had the same issue - I followed the following instructions and it worked beautifully.
First I deleted the .m4r file(s) in the ringtones folder of itunes. Then I rebuilt the library following these instructions:
http://docs.info.apple.com/article.html?artnum=93313
Follow these steps:
1. Quit iTunes.
2. Locate your iTunes folder.
* For Mac OS X the iTunes folder is stored in one of the following locations:
/Users/username/Music
* For Microsoft Windows XP and 2000 the iTunes folder is stored in
\Documents and Settings\username\My Documents\My Music\
* For Microsoft Windows Vista the iTunes folder is stored in
\Users\username\Music\
3. Open your iTunes folder.
4. Drag the iTunes Music Library.xml to the Desktop
5. Drag the following file from your iTunes folder to the Trash:
*
* Mac OS X: "iTunes Library" (in versions of iTunes prior to 4.9 this was called "iTunes 4 Music Library").
* Microsoft Windows: "iTunes Library.itl" (in versions of iTunes prior to 4.9 this was called "iTunes 4 Music Library.itl")
6. Open iTunes.
7. From the File menu, choose Import.
Tip: Do not add any music into iTunes at this point.
8. Navigate to the iTunes Music Library.xml file on the Desktop.
9. Mac users: Click Choose.
Windows users: Click Open.
After re-creating your library, any devices that you sync with iTunes (Apple TV, iPod, etc) will see your iTunes library as a new library and will completely resync."