I realize this is an old thread, but one solution that worked for me was changing my "game account" password to a different one than my "browser profile account." When I had initially set up both I made each of them use the same password. Changing the game password to a different one fixed my issue instantly. Whether or not this will fix everyone's issue is uncertain, but it seems the game launcher has some way of knowing the passwords of both accounts and this throws an error when the passwords are the same.
Hopefully this helps.
