iphone 3gs wifi network "unable to join"

since I updated my wife's iphone 3gs to the latest and greatest version she has not been able to login or "join" any wifi network. the phone picks up any and all networks but when you ask to join...it will not. anyone have any suggestions for the fix before we head off the the apple store.

i have tried several things pertaining the phones network settings but nothing has worked. the crazy thing is...it finds the wifi but will not allow it to join!!
thanks