"The parameter is incorrect" while copying pictures out of "camera roll"

My wife had a pile of pictures in her iPhone 3G "camera roll". After we upgraded her to iPhone 4, those pictures look OK in the "camera roll" thumbnail view, but every one looks black when we click on it. So, I figured that I would copy the pictures to my Windows 7 PC and put them into a different folder. But, when I try to copy pictures out of the "camera roll" into Windows (using the standard explorer view), I get the error "The parameter is incorrect" error on any picture that was restored from her iPhone 3G backup. Pictures that she has taken new using her iPhone 4 work fine. I tried deleting the "iPod photo cache", but that didn't help. Any ideas ??