QUOTE(John Solie @ June 10 2008, 03:31 PM)

I'm not in front of my editing machine right now, but I've had something similar happen. I'm flying from memory here, which could be faulty.
I think there's an menu option under "Tools->Cache->Purge cache for this folder" for purging the cache. I've also got the box checked to export cache files to the local directory. When I've done this, Bridge nicely thumbnails for me.
There's also a setting somewhere under the preferences for the largest file size bridge will process. I had to up this to some huge number (like 800MB) so that my album layouts would show (not that any of the layouts are that big--I just like seeing previews of my files)
Hope this helps!
Been a while since I used Bridge, all about Lightroom for me now. But I believe the answer from John is correct - purge the cache.
Regards,
Hugh