i go to my admin pannel on the main part of the Administration.Every time i try to make a super user this then goes to a blank screen why?

Its the same sreen i go to logg in as admin yet this is blank?
I don't no what im doinjg wrong can you plz help thanks.

I can make admins for the forum part in phpbb2 but just not admins for over all power.Its got me stumped ???