Essentially, the server is looking at your MAC address and deciding it doesn't like the credentials that are being sent along with it. For some reason, it believes the credentials (serial number and/or Device ID and/or signature) were different in prior sessions, so it denies access to the channels streams.
Make sure you disable the automatically configure feature in the epg updater after you allow it to configure your client or it will reconfigure your credentials and the server will be thrown into a tizzy when the new credentials are supplied with your MAC address. An authentication failure (like yours) will result. Beyond that, here are some trouble shooting steps...
http://iptvtalk.net/showthread.php?9506-Troubleshooting-Authentication-on-PVR-Stalker&p=119747&viewfull=1#post119747