This is my first really bad experience with Microsoft's new User Account Control (UAC).  Something caused our long-used and well trusted service account to be disabled.

After installing Windows Server Administrative Tools Pack so I can use MMC snap-in "Domain Users and Computers" (dsa.msc) on my local PC and after a few runas error 193, I kept getting the following error message:

C:\>runas /user:"domain\username" "mmc %windir%\system32\dsa.msc"
Ento start mmc C:\Windows\system32\dsa.msc as user "domain\username" ...
RUNAS ERROR: Unable to run - mmc C:\Windows\system32\dsa.msc
740: The requested operation requires elevation.

The solution was to call 'cmd /c' which tells 'cmd' to open and run the command supplied as a parameter, which is our mmc command:

C:\>runas /user:"domain\username" "cmd /c mmc %windir%\system32\dsa.msc"
Enter the password for domain\username:
Attempting to start cmd /c mmc C:\Windows\system32\dsa.msc as user "domain\username" ...


...now it works! :)