pkgmgr.exe /norestart /ip /o:"C:\WinToolkit\Mount;C:\WinToolkit\Mount\Windows" /m:"C:\WinToolkit\cInst_1\update-bf.mum" /quiet And before it runs that, it will check if the update-bf.mum exists. I've changed some code which cleans up directories better, that is the only thing i can think of which could cause the problem.