When running gpupdate (XP and above) and event ID 1091 ("The Group Policy client-side extension Security failed to log RSOP (Resultant Set of Policy) data. Please look for any errors reported earlier by that extension.") is logged, you might get rid of this error by typing in succession the following commands at the command prompt in the %windir%\system32 directory:
regsvr32 /n /i userenv.dll regsvr32 /u scecli.dll regsvr32 scecli.dll
Then run gpundate again and check the application log to see if the issue persist.