SBS 2011 only supports a single Network Card by design. Many of the HP servers that we sell our clients come with multiple network cards installed in them. Most people will simply connect one of the cards and then leave the other disconnected. The downside with this is that it can cause problems with poluting the DNS with nonsense IPs and that in itself can cause many things from slow logon to slow bootup of the server. Below you can see a screenshot of a server with two NICs. Local Area Connection is the primary NIC being used and as you can see is plugged into a switch. Local Area Connection 2 is NOT used but is left enabled. You can also see the binding order of the Network Cards with Local Area Connection 2 being above Local Area Connection. This is not a good situation nor is it best practice.
Solution is simple.
Disable any NICs you are not using – disable it in Network Control Panel. Furthermore – for good practice, I always ensure that the primary NIC is at the top of the binding order. This has given me more reliable servers than leaving the secondary NIC both enabled and at the top of the binding order. I recommend you make this your best practice too.