The installer is unable to connect to MySQL

The script

gallery3/installer/index.php?step=save_db_info

says:

"We were unable to connect to your MySQL server with the username and password that you provided. Please go back and try again!"

But I created a database and submitted the correct login information (I did that for other scripts very often successfully).

In the first line there is a PHP warning:

"Warning: ini_set() [function.ini-set]: A session is active. You cannot change the session module's ini settings at this time in .../gallery3/installer/index.php on line 32"

What can be wrong?

Manfred