Can't get the server version from anonymous user on WLS8.1

Hello everybody,
I'm trying Application Manager 6.0 with WebLogic 8.1 sp3 on HP-UX.
As stated in a previous topic: http://forums.manageengine.com/forumHome.do?forumGroupId=49000000002007&forumTopicId=49000003285132, I didn't set the following parameter -Dweblogic.disableMBeanAuthorization=true.
But, unfortunately, I have got this in my server log file:

<ExecuteThread: '2' for queue: 'weblogic.admin.RMI'> <<anonymous>> <> <BEA-000386> <Cannot get the server version, the request was from an anonymous user (Principal).>

I've also tried to add the above parameter, but nothing changed.

Thanks,
bye Stefano.