Are you sure this is actually happening while partitioning, rather than after partitioning? If the error message really says "cannot copy file," that's most likely to occur while installing (specifically, while copying files from the DVD to already-created partitions on the hard disk).
You haven't given us much information, but most problems copying files while installing are the result of bad installation media. So:
Since you created both DVD media and USB media from the DVD
.iso image and got what you believe to be the same error, it's most likely the
.iso image itself is what's bad (so the MD5 test will reveal the problem and you can re-download the DVD
- If you download a new
.iso image, MD5 test it, and find it's corrupted as well, you might try downloading via torrent, since the BitTorrent protocol checks for (and fixes) corruption as it's downloading. You mentioned that you had a similar problem installing at least one other OS (Backtrack). Most other operating systems also have MD5 hashes (or similar) available, and you can check to see if those downloads are corrupted in the same way.
However, if the MD5 test doesn't reveal errors, you should still check the installation media for defects. You may have two separate, defective writes, or a subtle hardware problem in the machine on which you're installing.
If this happens with other
.iso images, even if it includes
.iso images for other OSes, it's still worth running those tests, as there may be a systematic problem (for example, with your Internet connection) causing you to download corrupted
.iso files. There may also be a systematic problem (perhaps with your technique) causing them to be written and/or burned incorrectly.
Depending on the nature of a hardware problem, doing "Check disc for defects" (which applies to USB media as well as actual CD/DVD discs) may fail due to a hardware problem on the computer on which you perform it. That can be good, in that in combination with other information, it can make it possible to diagnose a hardware problem.
It also might be that, due to a problem downloading images, burning/writing them, or a problem with the computer on which you're installing, all installations have a high chance of failure, and that your one installation succeeded more due to luck than due to it being a different ISO image and installation medium.