If manually mounting images using imagex.exe gives you the error: "System could not find
specified file", then you might be missing the WIM filter driver on that system.
ImageX.exe needs to be able to load the WIM filter driver and it can be installed by using the WIMFLTR.INF to install it.
Browsed to X:\Windows AIK\Tools\x86 (Where X: = the drive WAIK is installed)
Right clicked WIMFLTR.INF and selected Install.