Problems with Windows XP ICS - Help Me!?

I have had my laptop networked with my Xbox 360 for a while using ICS. It worked fine. However, I have recently changed my broadband provider and the ICS network no longer works.

I have tried to select the Internet Connection Sharing box (Allow other network users to connect through this computer's Internet connection) but as soon as a click OK I get this message:

'An error occurred while Internet Connection Sharing was being enabled. Internet Connection Sharing cannot be enabled. A LAN connection is already configured with the IP address that is reqired for automatic IP addressing'

Does anyone know what this is and how I can make my ICS work?!

Many thanks!