Remote Registry Inaccessible to 2003 Server

VSS fails with the following error:

Starting guest agent
Cannot initialize information about the guest's system. Target host: [xxx.xx.xxx.x].
Cannot collect metrics about the guest's operation system. Cannot open sessions
manager's registry key. Win32 error:Access is denied. 

Typically this is simply meaning that the remote registry service is not running on the source guest virtual machine, or it is inaccessible due to firewall restriction.  

Make sure to check if remote registry service is running before trying advanced solution.