User with dba privs can't login to APEX, but can from SQL*Plus

I’m using Oracle 11gR2 XE. A user with dba privileges can’t log in to the APEX interface, but can from the command line with sqlplus.

I just created user:

CREATE ROLE administrators;
GRANT dba TO administrators;
CREATE USER superuser IDENTIFIED BY "root";
GRANT administrators TO superuser;

If I run cmd, type sqlplus and log in with “superuser”, I get access.

But the web interface (APEX) denies access with an “invalid credentials” error message.

What do I need to do to be able to log in on the APEX interface?