OK this is really boiling my piss right now.

Ever since I moved house and changed provider to BT Infinity 2 I've had a problem connecting to the wifi router.
Every time I shut the lid, the next time I open it up it tries to connect to the router but brings up the enter password box.
I enter the password but it then says: "Invalid Password"

I keep pressing the Connect button and sometimes after about 10 attempts it actually connects.
Other times it simply refuses so I go to System Preferences > Network and remove it from the list and then add it again and go through the same enter password routine until maybe eventually it connects.
Sometimes I even try restarting both the MacBook and the Router but same issue

Once connected it's absolutely fine.

My OpenBox connects fine, my Android phone connects fine, my wife's Chromebook connects fine as does her and the daughters iPhone, it just my MacBook thats having an issue.

Anyone had this before?

I'm using Yosemite 10.10.5