iTunes keeps losing movie thumbnails
I'm using iTunes on W7 Pro 64 bit, all been working fine until the v10 update. Ever since it has been having trouble remebering the poster frames I set for movies. Not all movies, just some - and I think only the ones imported after v10. I can set them, they're fine for a bit and then one day, all reset to the first frame of the film. Also when I reset the poster frames it often doesn't work first time - I have to open the movie in its own window, set poster frame which fails, close movie window, then reopen and repeat at which point it works. It doesn't work first time and always works second time. Weird!
It may have something to do with the fact that I keep all video files on a network (NAS) drive, although the older imports which don't lose their thumbnails are there as well.
Has anyone else had or cured this problem?
TP
Desktop PC, Windows 7