Hi Raj,
When you browse for tags in Management Console you are using the DCOM permissions defined for the user account you logged into the PCo Server with. The Agent Instance by default runs under the LocalSystem account, and many customers will not enable DCOM for LocalSystem.
If you are getting this error after Starting the Agent Instance, you will need to set up the instance to run under a named user account that has the desired DCOM permissions enabled.
If this condition persists after executing the agent instance with a named user, please log a support ticket so that our support team can investigate; provide a Verbose agent instance log and the description of the PCo and OPC Server DCOM settings for the named user as well.
Regards, Steve