This can occur when Informed Print is being used, but the Mac system does not have Pharos Notify installed, and/or communication from the server to the client Mac is not open on port 28201.
One can verify Pharos Notify is installed by going to /Library/Application Support/Pharos/ and looking for Notify. You can further verify that it's running by opening the Activity Monitor under /Applications/Utilities and looking for "Notify". Please note "notify" without the capital N is an Apple process, and not the Pharos software.
To verify the server is able to communicate to the Mac over port 28201, you may run a telnet test on the server using a Command Prompt:
C:/> telnet MacClientIPAddress 28201
Substitue "MacClientIPAddress" with the IP address the Mac is using. If you get anything other than a failure message return from the server in that command prompt, you've likely established a good connection to the Mac over port 28201, and in this case, port blocking is likely not the reason for the Notify failure.