rebuilding video thumbnails

I'm running XBMC Frodo nightly builds (just discovered them the other day) on my ATV2. In making the transition from Eden to these nightlys, somehow I managed to mess up my video thumbnails, particularly on my movie library. Many of the thumbnails are present, but many are not.

I have my video library set up as MySQL on my Synology NAS, connected via NFS, where each movie is in a separate folder underneath "/movies". All the needed artwork is still in each movie's folder.

In researching my problem, I came across something sayI even tried deleting the Textures13.db file, as well as the /userdata/Thumbnails folder, but the same phenomenon is still ongoing--a bunch of my thumbnails are missing.

What's the best way to proceed here? SHould I delete the /movies and /tvshows sources I've entered and redo the whole thing? I tried resetting the content to "None" and then "Set Content" again, too, but that didn't work either....

Suffice to say I'm confused, and I know I've probably gone about this completely wrong, but I guess I'm just asking for someone to point this lost stranger back toward the main road and I can find my way home from there

Thanks!