Hello all, i received this error 0×80070091 During USMT of windows 7 X64 (SCCM 2012 RC) 
After research, this is a known issue with x64: 
Just after the step Capture User Files and Settings, add a step "Run Command Line' with as command: cmd /c REG Unload HKLM\$DEST$Software 
Information taken from http://sccm.haas.se/?p=272 
Have a nice day