In versions 5.2 and 5.3, the main administrator cannot be edited, even when you are logged in as that admin. To fix this edit admin/selectoption.php
Line 17, currently looks like this:
$user = $userob -> authenticate("$Username","$Password","U_Username, U_Password");
Change that, to this:
$user = $userob -> authenticate("$Username","$Password","U_Username, U_Password,U_Number");