when trying to do a system repair/recovery and running “sfc”…you might get an error about a repair service being unable to start.

to get around this run sfc like this:
sfc /scannow /offbootdir=c:\ /offwindir=c:\windows

source:
http://social.technet.microsoft.com/Forums/en/winserversetup/thread/00580ff7-4412-459b-b176-c8a002ebd740