Cheers mate. Yeah, I have googled until I am blue in the face and seen this. Trouble is most of the fixes including this one are to fix the actual thumbnail. My thumbnails are all absolutely fine, it's just the small icon on the bottom right of the thumbnail and it's very intermittent. Bizarre really. Hmmm, trying to know the cause is like looking for a needle in a haystack. It might of been happening for a long time but I only noticed it recently.