It isnt really a common problem and so far 99% of people who post that the repairs couldnt start are able to have them run in safe mode with no problems, this is because their antivirus or a 3rd party program kept getting in the way of the repairs, but in safe mode those 3rd party programs normally are not running and so dont get in the way.
Thats why you didnt find any answer for that because the problem wasnt the program and safe mode normally takes care of it.
But of course getting some info from you will help a lot on finding out what is going on, what version of windows, av and post a screen of the error itself. I have to have some info to work with lol
Shane