Ok i know this is like over 2 years old but just incase anyone searching on the net has the same problem il provide the soloution for it.

Basically this problem can occour when you are using your own router rather than a sky router.

In the PPPoA settings on a router the you need to type in skys username and password which is in built to the firmware on a sky router they send out to you.

Log into your router (username: Admin Password: Password

Then click the following link and open the file into a text editor:

You'll be presented with a file that looks something like this:

ok for this perticular example

The username is: 00123A456B78@skydsl
and the password is: 1Ae203a0bb

hope this helps