I have been pulling my hair out with this problem. Windows Server 2008 installed on a physical machine previously flawlessly running 2003 Standard. Dual on board Intel Pro 1000MT NICs. Problem occurs with both adapters. Static IPv4, DHCP client service disabled. Cisco 2950 switch and Sonicwall firewall in front. Other machines running Server 2003 behind the same firewall and switch have no problems at all. I'm sure there will be more details required, but that's a quick synopsis.
THE PROBLEM- Regular connection drops for no more than a couple of seconds. This happens on all open ports. With RDP and all internet connections. Port 80, 25, 587, 32000, 3089, 110, everything. It happens in what appears to be 15 second based timing. For example 45 seconds, 60 seconds, 75 seconds. That total seconds between drops is random, but always based on 15 seconds. Enabling or disabling Power Saving does not have an effect. And the only network services currently associated with the adapter are IPv4 and Qos packet scheduler. With a website connection, it will only lose contact for the 2 seconds or so, but with RDP it sometimes attempts up to 2 times to reconnect. Any ideas would be greatly appreciated, as i have very few hairs left.