Gamelauncher doesn't like my password anymore

I had this happen to me once. I tried all sorts of solutions, like changing the email address associated with my account and then changing my password (old email didn't exist so I had to do that one first). Neither of those worked until I used the email address in place of my ID and then used the new password.

I'm not sure if you have the exact same issue though, since mine only occurred after I had refused the game's suggestions of changing my password for several years.