Problem using capital letters in games.

Are you sure the gamer tag isn't already in use by someone else who is using a capital letter? Using capital letters is no problem.

First, check to make sure you aren't/ are, using capital letters where needed. Passwords are generally capital letter sensitive.

The Lagg is some letter are not in Capital but people see it in Capital

I had a problem similar wouldnt allow me to use capital letters on website using pc or ipad but worked fine when i did it using my phone what are the odds

Maybe it's an inactive gamertag that someone created but does not use any more, on the old gamertag system. If you wanted that gamertag why don't you try it with capital letters or some numbers too see if that's available, if you don't mind the capital
letters and numbers that is.