If purgaing the cache does not work you may have to delete the cache file manually.
Do you have cache exported to Folder option checked?
If so you really have two cache locations. The only way to clear both is to go to Tools/cache/purge cache for xxx folder.
You will have to do this for each folder.
Thanks for the reply.
Lucky for me that's just a few folders that I need to check for an exported cache. That's only because I use that computer as a "way station" to collect image files on location, and import them later to my main machine.
Manually deleting everything seems to have worked, but I'll need to wait while all thumbnails are re-created. Bummer. Wastes my time. Not conducive to sales, believe me.