I bought a WD My Passport (Essential) 500GB a few days ago. I needed it to move my old files from my Pc to my new iMac. I connected it to my Pc and installed WD Smartware on it so it could be used and then moved over my files, no problem. Then I connected it to my iMac and I moved the files from the hard drive to the computer, but I can't erase any files from the hard drive when it's connected to my Mac, and I can't move any files from my mac to the hard drive. How do I fix this?