Thank you Fred, Terry, Ray, and Mike for the advice and hints from my two earlier problem posts.  It took me a while to go back a few weeks and reconstruct the sequence of stupidity that caused this problem. But as near as I can figure out I did some combination of the folllowing things.  First, I imported a very large number of new photos (about 400) and put them into a single folder - which I don't normally do.  Then I followed my normal workflow and created a basic filter (autoexposure and minimum sharpening) just to let me preview all of the photos. So - I said "apply filter to all photos in the queue" - and right after I said ok - I SHUT DOWN QIMAGE to go work on something else for a while.  Obviously, I shut Qimage before it had updated all of the thumbs and it was my next Qimage sessin where I had the first hint of problems - with thumbs refusing to show and Qimage hanging.  Then to make matters worse, I used explorer to move some image (and the corresponding flt files) to other folders. If that wasn't bad enough, I then opened Qimage to one of these folders to preview some photos, and while still open, I edited in PSE (something else I seldom do).  Along the way, I did a few other things that didn't help either - not worth going into it all.  Anyway, everything is now stable again; I deleted and replaced some folders, rebuilt thumbs all over the place