error 5 on services.msc / exception with ServiceController

I have a mysterious problem at some client.
I can't remotely control the services.

When I go to
control panel => administration => services
I launch services.msc to monitor the services.

If I right clic (on XP) on 'local' (on the left, local for my pc) I could
connect to a remote computer.
now every time I try any computer at my client (who is logged as an
administrator) I get an error 5 'access denied'

although it work OK at the office.

also I tried (with the .NET SDK) to call
System.ServiceProcess.ServiceController.GetService s("a_computer");
and I get an unauthorized access exception too.

what should I do ?
what could it be ?

this client has a "Novell Network" (whatever it could mean, because it's XP
machines after all)
any ideas tips ?