Windows Server 2008 as PPPOE Client

For almost three months, i am having problems with a Windows Server 2008 box configured as a PPPOE Client and a proxy server (TMG).

The issue is, the employees complain that there's no internet connection while, the High connection object in Windows Control pannel shows as connected...

I don't know if anyone faced that same problem before or  not, and if yes, what was the solution?

Thanks in advance!

Lotfi BOUCHERIT