Nikhil,
To add to Selva's check, I would suggest you to install PCo on the same machine as your OPC server which is the most recommended and problem free option.
If your OPC server machine is not compatible for PCo installation due to size and security constraints (as in some CNC machines with PC units), work tightly with your network admin to remove the possible network constraints like
1. Firewall restricted ports are opened as required,
2. Local Static IP addresses to the systems separated by different VPNs separated logically or physically,
3. Common service user is created with required network access privileges and used for authenticating PCo to OPC Server connection.
To avoid all these issues it is suggested that you go with PCo installation on the OPC server system.
With regards,
Ponilango P