i also face this problem.
i fired SDE,he sent his chap,
he says you have to use it in bridge mode.
and after his bridge mode ,its working.
i used to face ATM authentication errors and all.
he was giving me stupid reasons like you are running it on inverter
next was your wiring is messed up.
but all the while i used to have solid DSL indicator and no internet indicator.
but his trick of ridge mode works flawlessly.
his latest excuse is your modem is old.
yes it is old like say 3 yrs old.
does it make any difference?