S4 wi-fi won't connect to S2 hotspot

[Stuart Holmes]

I've bluetooth paired my S2 & S4 and set the S2 mobile hot spot to 'on'.
The S4 wi-fi is on and it can see the wifi network provided by the S2 but when I select ''connect'' the dialogue just vanishes and I'm back at the screen which says it can see the S2's network with strong signal 'saved & secured' but not connected.

Can anybody pleas tell me what am I missing in my effort to make the S4 connect to the S2's wifi hotspot?