Hi. I also purchased the Seagate Backup Plus for my iMac and copied a selection of folders to it. I didn't want the entire iMac backup as I have a drive specifically for that via Time Machine. Anyway, after I copied folders to the new Seagate Backup Plus, I moved to my MacBook to copy files from that but it wouldn't let me.
I never had to format the drive when I initially bought it and used it on the iMac. I don't see why I would need to format it to get it working on both machines when it already works on one. There must be some option to select that I don't know about.
gbrew345, did you find an answer?
The below response from popatim says they believe it was originally formatted for PC, but the box and included tutorials say its for both. Plus it works perfectly on my iMac. Its just the second Mac it has restrictions… Help anyone???