Hi there, Ill explain once more:
You need to change the mac-address on the dlink to the same mac-address as the old modem. You can do that by loging into the dlink command line interface with telnet and use the macaddr command.
The problem I had was that the mac-address that the DSL interface gets is a value of 2 more than what you entered with the macaddr command. To fix this you take the mac-address from the old modem, subtract 2 and enter that value in the macaddr command via the command line interface.
Hope it is a bit more clear now.