sidero,
I do not know much about Avira, but when you run a remote elevated command against a machine using: "C:\Program Files (x86)\Avira\Antivirus\avcenter.exe" /STARTUPDATEE (Does it work)?
In my environment, we run our browser session for accessing lansweeper as our admin acounts (also login as our admin accounts).
My action for a similar command looks like this:
cmd.exe /K {actionpath}psexec \\{computer} /c {actionpath}whatever.bat
Should "STARTUPDATEE" switch have two "ee", just asking, but didn't want you to spin wheels on a typo.
Best of luck