Two iPhone's in the house, a model 4 (on iOS 6) and a model 5 (on iOS 7), can not connect to the home WiFi network, but can connect at the Apple shop. All other devices on the home network, including desktops, laptops and Android's, are fine.
The error message is displayed about 0.5 seconds after hitting "Join", and is simply "Unable to Join Network".
Trawling forums the advice seems to be to a combination of resetting the network settings on the iPhone and turning the router and iPhone off and on again in various orders.
However, this does not work.