Task Sequence Command Line to Unregister DLL Not Working...Won't Run As Administrator

Hi All,

I'm trying to unregister a dll by creating a Custom Task Sequence using the command line "%SystemRoot%\System32\regsvr32.exe" /s -u "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll"

SCCM is reporting success, however the DLL isn't being unregistered on the client machines.  If I manually run the command on a client machine as administrator it works.  I have specified that same administrative user in the Custom Task Sequence.  These are Windows 7 machines, so my hunch is it has something to do with UAC, but I'm kind of stumped what to do here but feel like I'm missing something obvious.

Thanks!