Let me preface this by saying I have spent the last day scouring the internet for solutions to my problem. I have tried every option that I have run across and have had no luck in resolving my problem. As a last resort, I'm turning here in hopes that you can be of help. I have a 2012 Macbook Pro running Moutain Lion. I use an external HD for my time machine backups. I am having an issue with Time Machine not functioning. The initial error message I receive when I attempt to use TM to backup is: "Time machine couldn't coplete the backup to Rick's backup disk". "Unable to complete backup. an error occurred while creating the backup folder". I searched the forums and net and found several things to do to try and resolve this issue. Disk utility will prompt me that it cannot unmount the disk and will not let me erase, or re-partition the the hard drive, so I switched it over to an older macbook of my girlfriends and am successfully able to erase, and re-partition the drive (using disk utility) as suggested by several forum postings I have read. I am able to run disk verify and disk repair and both say the disk is "ok" with no issues. The moment the erase and partition is done, her computer prompts a message : "Would you like to use this disk for Time Machine Backups" which tells me it is working properly. When I move it back to my macbook pro and attempt to run TM backup, it will now work and copy about 10g of my 120g before shutting down with this error message: "Time Machine couldn't complete the backup to "Rick's Backup Disk". An error occurred while copying files. The problem may be temporary. If the problem persists, use disk utility to repair your backup disk." If i attempt to re-run TM at that point, I get the original error message: "Time machine couldn't coplete the backup to Rick's backup disk". "Unable to complete backup. an error occurred while creating the backup folder". If I move the TM back to my Girlfriends computer and attempt to run TM, it will function properly and backup her entire harddrive. When I erase and try again on mine, I always end up back with the same issues. It's clearly something in my macbook that is screwing it up. Can anyone please offer some help! I'd be much appreciative.