Thanks for the response JFX. I was running wimlib-imagex on a custom WinPE 3.1 build - more specifically a customised boot.wim from a Windows 7 SP1 iso.Will try again when I get the chance with a basic WinPE 3.1 WAIK build with just wofadk.sys and the following registry settings added - Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\WofAdk]"DebugFlags"=dword:00000000"DependOnService"=hex(7):46,00,6c,00,74,00,4d,00,67,00,72,00,00,00,00,00"Discription"="WofAdk Mini-Filter Driver""DisplayName"="WofAdk""ErrorControl"=dword:00000001"Group"="FSFilter Compression""ImagePath"=hex(2):5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,\ 74,00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,64,00,72,\ 00,69,00,76,00,65,00,72,00,73,00,5c,00,57,00,6f,00,66,00,41,00,64,00,6b,00,\ 2e,00,73,00,79,00,73,00,00,00"AutoAttach"=dword:00000001"Start"=dword:00000000"SupportedFeatures"=dword:00000003"Tag"=dword:00000002"Type"=dword:00000002[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\WofAdk\Instances]"DefaultInstance"="WofAdk Instance"[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\WofAdk\Instances\WofAdk Instance]"Altitude"="40730""Flags"=dword:00000000Regards,Misty