First, test your login details by signing out of your GameHouse account on the website and then sign back in.
If you cannot sign in on the website, reset your password by clicking on the Forgot Your Password? link and follow the steps in the email to reset your password. Now test your login on the website again. If you can sign in, continue to the steps below.
1. Untick the Remember Me box in the game window.
2. Sign out from the game window, then click on Unlock Purchased Game. 
4. Sign in using the same email address and password that successfully worked when logging in on the website, ensuring there are no spaces before or after your email or password. DO NOT tick the Remember Me box just yet!
5. If successful, upon opening the game next, you can re-enter your login details and tick the Remember Me box to save your login details in the game window.