Cannot Connect To WiFI

I have several devices connected to a wifi. I have two Macbooks connected and now one of the Macbooks will not connect. I'm sure it's the correct password because it works for all the other devices. Everytime I try to connect, I get this:

The Wi-Fi network "xxxx" requires a WPA2 password.

I've restarted the machine, restarted the router, removed the network from the machine and then tried to connect. It just refuses to connect.

What is going on?

The older Macbook is a 7,1. The newer one is 11,1.

Any assistance in resolving this is greatly appreciated.