When that happens (image doesn't display) I usually load the (.jpg) image in an image editor, like
irfanview (see
http://www.irfanview.net/ ), and just resave it, overwriting the previous copy.
Then rebuild the .imp and it usually shows up afterwards.
I don't really know the reason, but my default .jpg viewer (ACDSee v1.0) also has problems displaying similar/recent images so perhaps it's a jpeg encoding issue.