Need Help

[#1]

Hi, I've been getting the following message recently:
Authentication Failed... 

Your Internet authentication failed.
Before you can authenticate yourself, you have to login as a more privileged user.
The only way i can get rid of this and get back online is by restarting my Laptop which works for another 30 mins then the same again.
Any ideas on why its happening and how to resolve?
Cheers

[#2]

What happens when you get this message? Does your connection drop? Or are you actually using a web site at the time that needs authentication to get in? That sounds like you are losing some kind of user privelege for a secure site rather than losing the internet connection. More info required please. 

[#3]

Or alternatively an error message from your router, what modem/router are you using?

[#4]

my connection drops and the message is from the Thompson gateway.
Using the free thompson modem that i got when i joined plusnet. (thompson tg585 v7)
thanks

[#5]

Questions... Which lights go out on the router when this happens? Do you have to reboot the router as well as the laptop or just the laptop? Do you have any third party software on your laptop which monitors the connection somehow or the state of the router?