It seems no connection to the database has been created.
Have you set properly the fields of the "configuration.php" file?
If you already had, you may want to create a connection by yourself.
Check the mysql_connect function and call it before using mysql_real_escape_string.
If you are using POG you'd better read the generated code and realize it will
call mysql_real_escape_string by itself, there's no need for you to do it.
--
The most likely way for the world to be destroyed, most experts agree, is by accident.
That's where we come in; we're computer professionals.
We cause accidents.
(Nathaniel Borenstein)