TO check firewall
Apple->System Preferences->Security & Privacy->Firewall
My primary question with AFP is when you are connecting -what account are you using to login to the remote server – the local admin?
In the old compressor it was quite evident how to reset the services. In the new one I have no clue. You can try the command line: qmasterprefs -reset
I have no way of testing this as I do not have a system with only Compressor 4 installed.