Thanks for your post and welcome to the forums. It's great having you on board with us in the Community.
I'm sorry to hear that you are having an issue signing in to TV Go on some devices. It may be worth checking that you are typing in the address for the username instead of using any predictive or suggested text as sometimes this can add a space which will invalid the address. This can also happen if you've 'remembered' the details.
Are you able to sign in to the My VM app using the same details?
Can you please provide a screenshot of the error message so we can check this too.