New Windows Service Monitor

Hello,

I am having problems adding any Windows Service Monitors to one of my servers. It's a Windows 2003 server. I know I am using the right username (domain\username) and password because if I add the user to the administrators group on this server, it works fine. However if I remove the user from the administrators group, it ceases to work. It gives me the following error:

Error # Access denied

I know the user needs the following rights, which I have given him:
1) Allow log on locally
2) Log on as a service

I've tried adding the user to EVERY other group on the server and none of them grant him the right to add the service (always the same error) (except 2 groups, both of which are sub groups of the administrators group).

I've already tried the suggestion in the following forum article:

http://forums.manageengine.com/forumHome.do?forumGroupId=49000000002007&forumTopicId=49000002635487

however, it didn't fix the problem.

I know this configuration should work since I've got another server which I monitor, on a different domain where this works. (another Windows 2003 server, user not part of administrators group, same privileges)

My questions are as following:

1) What exact rights are required on an account to allow OpManager to monitor a service on the box?
2) Am I missing anything?

Tibal