This is an issue that cropped up for me with the new 6.3 update. I'm trying to run a batch file that creates the Scheduled Task to allow CCleaner to run without UAC:

schtasks /CREATE /TN CCleanerSkipUAC /TR "c:\rcs\cc\CCleaner.exe $(Arg0)" /SC ONCE /ST 12:00 /RL HIGHEST /F

I can run the batch file just fine manually, but when I run as system (and redirect errors to a text file) with an agent procedure I get this error:

ERROR: No mapping between account names and security IDs was done.
(16,8):UserId: