Couldn't unmount disk

Question

OK so here's the deal, I had windows 8 installed using boot camp, Then when I went to uninstall it using boot camp, it gave me an error message, when I closed everything, I opened boot camp and the remove windows 7 option was no longer there, it was install windows 7, so I opened disk utillty and there wasn't a boot camp drive, however, when I went to partitions, boot camp wasn't there but macintosh HD didnt take up all the space and there was a grey area beneath the Macintosh HD, I dragged the Macintosh HD to the bottom and clicked apply, I got an error meassage which I solved by repairing the disk. So when I try it again, the process progresses more and then I get another error message that says couldn't unmount disk. All of this done from the Recovery partition. What Im going to do now is put mountain on an external hard drive and boot from that and try again. Guys please HELP AND REPLY PLEASE!!!!!!!!
This is the grey area I was talking about, I tried repairing macintosh HD but I still get the same message

Answer 1

I had a similar problem as the thread starter, and was able to fix it by making a bootable Mountain Lion Recovery Volume on a USB stick, as Courcoul suggested above (http://support.apple.com/kb/DL1433).
I had removed bootcamp and the associated partition from my Macbook Pro running Mountain Lion, and I wanted to reallocate that space on the hard drive to my main Mac partition.
The bootcamp assistant had failed halfway through the process, and it could not extend the partition to include the unallocated space ("partition failed"). It had also created errors on my main Mac volume (when scanning with Disk Utility).
1) The Disk Utility inside Mac OS was not able to repair the volume, so I had to boot from the recovery partition (cmd + r during boot), and then repair them. This would let the errors be repaired, but still I would get the error "Disk Erase failed with the error: couldn't unmount disk" when I was trying to resize the partition to include the unallocated space.
2) So Finally, when booting from the recovery USB stick, and using Disk Utility, I was able to resize the main partition to the full size of the hard drive.
I think the error "couldnt unmount disk" was due to the fact that somewhere in the process it said it was trying to "relocate the recovery partition". So I assume that if you boot from this recovery partition on the drive, it cannot do this part, and the process fails.
Thank you all very much! Your comments were really helpful. I hope my explanation is useful to someone with the same problem.