I have a similar issue from time to time. For some reason when it happens to me, it says my connection is secured with WEP (its actually WPA2) and it wont let me connect to it or the open "guest" signal from my router either. Sometimes turning off wifi and turning it back on again helps, other times I just have to wait. The other night it went on for a couple of hours. No idea what the cause or solution is though.