I've spoken to our development team and apparently my theory about the registration server is incorrect - the server doesn't actually check that your date matches its date.
This error must mean that PAH can't connect to the registration server, and that is normally a firewall issue.
Try disabling it temporarily while you start up.
If that helps you should be able to set an exception for PAHud.exe in your firewall configuration.
Please see the Firewall Guide - this refers to PT3 but the same principles apply.