back up problem

It seems to be pretty clear what it says.

I had this problem before and for me it was the 100MB system reserved partition. For whatever reason, it only had about 40GB free.....and then it seemed to have cleaned itself up and was well over 50GB once again. Once that cleaned itself up, my error went away.

No, you don't have to reinstall. Perhaps just reboot. Seriously, my 100MB system reserved partition fluctuated and dropped to less than 50mb. But a few minutes later, it was back to over 100mb free. I have no idea what was using that space.

Go into disk management, assign a disk letter to that 100mb partition and see if it's under 50mb. I would bet it is for some reason.

If the drive is full....that is the problem. You dont' have 50mb free and therefore cannot make the backup of the drive. That drive really shouldn't be full. i want to say that mine when working properly usually has about 80mb free.