I was having constant disconnects with Win7 Ultimate using Nvidia Network card.
After many attempts to remedy I ran across this post that fixed it for good.
Have not had this error for about 3 weeks now.
nVIDIA nForce 590 SLI AMD (MCP55PXE)
SOLVED Default Gateway Unavailable
I thought I would share a little fix for a problem I have been having with Windows 7 Professional, both RTM & Release.
I was having issues with Windows 7 intermittently dropping connection. After about 3 or so minutes, especially during heavy TCP activity, my NIC would loose the gateway settings and drop to a limited connection. Performing the built in troubleshooter would correct the issue, only to have the connection drop again within minutes.
After a little bit of research, it turns out that my NVIDIA nForce Drivers (the most recent ones from NVIDIA, and the Microsoft ones), were the source of this. I attempted to use NVIDIA's signed drivers and still had the same issue.
Turns out there is an issue with a driver setting in both that is causing this disconnections. If you go in to the driver settings for the NIC, and under the advanced tab there is a setting for Receive side scaling set to be enabled by default. By disabling this option, my network connection came back alive and has not lost connection yet.
Hope this helps anyone having this issue.
My Chipset: NVIDIA 590 SLI AMD