"You are currently logged on"

I am trying to use case designer. So I create a new Oracle user from sqlplus. I grant dba to it. Then I log onto sqlmenu50, and grant "Administrate" to the new user, and assign the CMAN role to it. Next, I run Case designer, try to log on as the new user, and get the following message:

ORA-01075: you are currently logged on

Anybody knows what on earth is going on? There is no way this new user is logged on from anywhere!!!

-- 
Ivan Ordonez-Reinoso               |"America es una, morena y alegre,
iordonez_at_magnus.acs.ohio-state.edu | es voz y esperanza de los valles verdes"
iordonez_at_cis.ohio-state.edu        |                           - Galeano