If you are trying to connect to a remote OPC server from Windows XP SP2 and you are getting the message “DCOM was unable to communicate with the computer using any of the configured protocols”, then think about the additional security features and firewall configuration provided by Windows XP Service Pack 2.

Let’s consider the following points while configuring XP SP2 for OPC communication.

• “Turn Off” firewall only for testing purpose (OPC client should work if firewall is “Off” and DCOM settings are correct). 
• If firewall is “On”, proceed with the following steps.   
  • Goto “Exceptions” tab and select “Add Program”. Add all OPC Clients & Servers and OPCEnum.exe to the list.
  • Select “Add Port” and add TCP port 135 (which is required for DCOM)
• Start DComcnfg.exe and select “COM Security” Tab.
• Edit the limits for “Access Permission” and provide Local and Remote access for Anonymous Login.
• Edit the limits for “Launch Permission” and provide full access to “Every one”

Hope this info will help to solve your OPC issues from Windows XP SP2 clients.