"I'll try that too. Its not in all folders. The root material folder crashes when I switch to thumbnails. If I do that to a sub-directory, it typically wont crash.
I think its a material because as I turn the thumbs on, as they…"
"If you're getting crashes on everything-- then the thumbnail viewer you've got my be bad. You could try re-registering the one you've got (using the steps outlined by Rich above)-- or try grabbing a new one."
"It's possible, although the thumbnail previewer has some code in it which makes it difficult to actually crash, even with a bad material. (Yours clearly is crashing). One way to test is to move some materials to a new folder and…"