Vista - Shutdown process on remote pc

Hello,

I posted this message already in microsoft.public.vb.com. Apparently, this
is a vb6-only group.
That's why I cross post it in this newsgroup.....

I'm trying to shutdown a process on a remote machine.
To achieve this I use the ManagementObject class and the associated options
(username, password, authentication, impersonation...)
When I run my code on a pc that's logged on to a domain, there is no
problem.
If I run the code on a pc that's in a workgroup, I allways get an error
message like 'access denied....'.
In the eventlog of the remote pc, there are some entries in the security-log
about the user Guest that's trying to logon to the machine. Strange, because
I provide the managementobject with a different username and password.
Some of you guys any idea what's going wrong????

Regards,

Q