Edit : CTRL-V works to paste the JSON details and the contract address - Hurray.
When I click OK it now says "Not a valid address".
I was just about to say, try Ctrl-V. I don't get a right-click paste option either using Mist (essentially the same as Ethereum wallet, I believe).
Did the contract address copy/paste completely?
0xAef38fBFBF932D1AeF3B808Bc8fBd8Cd8E1f8BC5
Edit: Make sure there's no extra characters or spaces before/after the address.