SQL Server Management Studio Activity Monitor will not run against our
production SQL Server 2008 Standard Edition SP1 Machine. It returns the error
"The activity monitor is unable to execute queries against server <server>..."

With the additonal information:

"Unable to find SQL Server Process ID <ProcessId> on server <Server>
(Microsoft.SQLServer.Management.ResourceMonitoring )"

The OS of the Machine is Windows 2003 R2.

ARITHAbort is not on by default.

The machine was recently virtualised and is running on an ESX 3.5 host.

Activity Monitor works on our other SQL Server 2008 Standard Edition
Instnces on other Machines (Windows 2003 R2/Windows 2008 R1).

Sorry I forgot to say that all machines are 64bit and rnning 64 bit versions
of SQL Server.

Any assistance would be much appreciated.