I recently downloaded the apk files to put the google play store on my sons fire tablet. All was a success and it seems to work as it should for the most part, with one exception that I need to remedy...

I installed the apk files and then signed into my google account to mess around. Here in lies the problem...when I try to log into my sons account, it will not let me. It says I need to log out of my account, but when I go to "manage accounts" the screen blanks and goes back to the home screen. So...I can switch users on the google apps on the tablet. Any idea?