ORA-01017 Invalid username/password - Password/Username is correct

Question

I have created an oracle database on the Application express from oracle database 11g express edition, now while trying to connect to it through toad for oracle (or visual studio) I get the error

ORA-01017: Invalid username/password;logon denied.

I use the same username/password to connect to the application express and get acces to the database. I don't know what's wrong.

I changed the tnsnames.ora:

OFFICEMEMO =
    (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = (my host))(PORT = 1521))
    (CONNECT_DATA =
      (SERVICE_NAME = XE)
    )
  )

but I don't think this is the problem because it already says invalid username/password.