We use a domain with .1X authentification I start the service Wired Auto Config and set it as automatic . The service starts and the Tab Authenticiation is on . I Do all my setup and the network works fine. If the PC Stays on all night the authentification tab disappears but the service is started. The only way to get the tab back is to stop and start the service. Can anybody helP!!

There could be 2 possiblity 1. Bad NIC drivers 2. Anti Virus Software So, please update the NIC and remove the AV software and try. Update the hotfix http://support.microsoft.com/kb/976373

I tried both and still the same problem after lunch.

Did you try the hotfix?