Configuration of the Windows Firewall is the same for both client and server. For troubleshooting, it would be best to turn off the firewall, get everything working, and then turn it back on.
If the firewall is required, go to the firewall’s Exceptions tab and review the following:
All OPC client and server programs on the local machine need to be added to the Exceptions tab. The program to add for the OPC client is:
NiagaraRelease\nre\bin\niagarad.exe
Add TCP port 135.