I have this problem on a fully updated windows 7 VM, guest of vmware fusion in mac. I have the vmware tools installed, and there are no updated drivers available, nor any updated version of fusion.
I find, that if I simply disconnect & reconnect the network adapter or cable, then the problem goes away. I think some of the other people posting to this thread, saying things like reinstall drivers and reboot the computer, might be experiencing the
same thing. If they only rebooted or only disconnected/reconnected or disabled/re-enabled their network adapter, they would probably fix it that way too.
Althesame, the problem keeps coming back, maybe once every day or two. It's caused by something, but I'm not sure what - perhaps sleeping, or disconnecting the NIC and reconnecting too quickly or something... not sure.
For now, I'm just going to use the occasional disconnect & reconnect network cable solution.