Performance monitoring from a remote computer

I am using a tool to monitor various services and statistics on Win2k3 servers.  The tool runs on a workstation - which is important because of course one of the main purposes of the monitoring is to get notified if services stop abnormally or if the server itself freezes or goes down.  Normally there is no problem with doing this, using an account that is a member of the Administrators group. However, I'm having a problem with one particular server in one of my domains.  This server was upgraded from Win2K to Win2K3 about a year or so ago.  I was previously able to monitor it with no problem.  Now my software cannot access the machine and when I try to connect remotely to the performance monitors I get a message saying "Unable to connect to remote computer."  I can, however, run performance monitors locally on the server, so it's not a problem with the perfmon program itself.

I've checked the permissions per MS knowledgebase articles and also turned off media sensing on the gigabit NIC per MS.  Still no joy.  Any ideas?

TIA,
Deb