Dynamic Permissions

Hello Everyone,
i have a little problem that I have not been able to find a solution :/
$_SESSION["UserID"] = username field on the database since I am using this on many tables I didn't want to display the email address but instead i wanted to display the name of the user logged in, this also works on the display logged on as: I wanted to show the name instead of the username.
So i modified the login.php this line and change it to this
$_SESSION["UserID"] = $data['name'];
so now the $_SESSION["UserID"] displays the name which works fine. but on the admin area in the section assign users to groups the list of usernames is displaying the emails, I assign everyone to the admin group. but then when i logged in, the menu is blank. so i had to go and check the data in the ugmembers table and everyone was there with the -1 GroupID. so what i did is that i had to add manually the name and set it to GroupID -1.
I hope this makes sense.

Thanks