Problems with Time Machine and WD My Passport

Hello everyone, I have a Macbook Air, running OS X 10.9.4, yesterday I bought an external hard drive My Passport for Mac 2TB, initialized in Mac Os Extended, I tried to back up with Time Machine, but arrived about 12 GB crashes and I get the message “an error occurred while copying the file. problem may be temporary. If the problem persists, use disk Utility to repair your backup disk.”. I have tried several times to repair the disk and repeat the process, but the problem persists. I then tried to connect another external hard drive and I tried to do the backup, but the same thing happens, the problem should be in the Mac. Could you help me? Thank you.

Hi, be sure to connect the Passport directly to the USB port on your Mac, using  USB extension cables or USB hubs can cause power inconsistencies.