potential problem? transferring 7D pics to HD

I wouldn’t bring this up except that it has happened at least twice to me. I transfer files directly from my 7D to the computer on a USB cord. I don’t have a working CF card reader at the moment. For some reason I transferred a couple of hundred photos at least twice recently and found that they didn’t all transfer. For example I transferred files 1 to 200 and found that files 34 to 60 never made it. I could not have missed selecting them because they were within the files selected.

Sometimes it takes 2 or 3 tries to get everything transferred and then of course I have to double check that all the jpegs and raw files are accounted for. I don’t doubt that this could be a Microsoft problem. I am using Win 7 on a Sony laptop, a setup I have had for over a year. I was just wondering if anyone else has noticed anything similar happening.