I found exactly same problem on my motherboard ASROCK n68-s3 ucc with AMD Phenom II 810 and 8GB DDR3 RAM as on the 1st post. I have tried even to update the driver from Windows update service, however, it doesn't help. By the way, it's regarding situation, where NIC try to obtain address from DHCP server, if you enter static IP, it works fine. I think that this is relating to driver or nVidia chipset architecture itself, which is relatively old and I can't understand why new motherboards still use it. I can't use static IP in my network enviroment, so I decided to disable onboard LAN and use PCI-E ethernet card, it solves the problem.