It was a common problem using 6.5 Info below from:
http://www.adobeforums.com/cgi-bin/webx/.3bbb6d59/6
“Using some image file formats within Premiere is actually a Windows system level problem, and Windows loses track of the internally decompressed version of the image -- the problem will change depending on the size of your images, the status of your swap files, how recently your system has been rebooted, et cetera. Best to avoid jpegs, compressed tiffs, psd files, and any other compressed image file.”
So if you can batch convert your jpegs to uncompressed tiffs or bitmaps, this will solve your problem. Are you able to do this?