snow leapord time machine backup hangs

I know that the iMac is old, but it boots fine. Photoshop started having issues last week, which is why he wants to revert to the way it was before it was acting up. He has a brand new Mini that he uses on the internet. The iMac is mainly for Photoshop, iMovie, etc, which he claims that it runs better than the mini. He needs an older Mac running snow leapord, because of the graphic work that he does, which needs to have the scroll arrows. The time machine drive is only two years old. I can try running disk utility remotely from the mini to check the iMac's drive.

This morning, the progress bar was gone, and the following enigmatic message was displayed: "You can’t copy “System” because it has the same name as another item on the destination volume, and that volume doesn’t distinguish between upper- and lowercase letters in filenames."