Try the following steps, on your phone, and see if this resolves the problem.
First option...
Go into the wifi settings.
click on the accesspoint and remove the password.
Now re-enter the password.
If the above doesn't resolve the problem, try this second option...
Type *#*#4636#*#* (*#*#info#*#*).
Tap "wifi-information" and then tap "wifi-api"
Now tap "disconnect", then "disableNetwork" and finally enableNetwork"
You should be good.