Answer at last--database version matters

I just had this problem, getting error: ORA-24315 no matter how I tried to connect.

I searched the web for hours, but didn't find the answer.
I figured it out, and will share, though it's a bit embarassing.

I originally downloaded/installed the Ora11g version, but the database is 10g.
I installed the 10g version of cx_Oracle, and the connection worked...