The two things that I ran into when using the QV User Manager were making sure you use the correct version for the version of the QlikView server. Also ensuring that the server name is in the config file correctly (under end point address). I would also double check the Active Directory group that you have created and added the user running the task to - this needs to exactly match what is expected by the routine.
The syntax I am using to call the exe is this:
"E:\QlikView Documents\Power Tools\Qv User Manager 11\qv-user-manager.exe" -l CAL
The different syntax for the parameters may also have a bearing.