dual nics

I have 2 network cards in a MS 2003 web edition server. NIC A has a static IP and is connected to my LAN and is working just fine. NIC B has a static IP and is connected to my DMZ. The problem is NIC B stops sending and receiving packets but it doesn?t disable its self so I?ve just repair the connection and it works fine for 6 hours or so.

The system detected that network adapter Intel(R) PRO/1000 PT Dual Port Server Adapter #2 was connected to the network, and has initiated normal operation over the network adapter.