From digging through Microsoft's forums, seems this problem is fairly common and is complained about often. I have several Win7 systems and have never seen this, but there does appear to be a manual fix.
You need to use regedit to modify your registry to remove these networks.
***The only working solution found from MS forums follows***
Before you do this make sure do perform a back up of your registry.
Do a search for the SSID name in registry and delete every folder that the string is located in, continue to search the registry until it returns with no more matches.
Restart your system. When the system restarts, those undesirable networks
should no longer be there.