Unable to edit images from specific date range

When trying to use the WP image editing features I am unable to edit images from posts that were posted during an arbitrary 9 month period in 2008. About 400 posts are effected, no image that was posted during those dates can be modified by WP. For instance, WP is unable to create thumbnails based on these images etc.

Images form before and after the affected time period work fine.

Any help would be greatly appreciated.