Installer - Database Connection fails

Hi,

i'm trying to install D6.6. In the Database Configuration Page i insert DB-Name, User an Password an i'm getting a Error like this: "Access denied for user 'username'@'%' to database 'database_name'".

If i try this small Script everything works fine:

<?php
$mysqlhost = "localhost";
$mysqluser = "username";
$mysqlpwd = "password";
$mysqldb = "datenbank";
$connection=mysql_connect($mysqlhost, $mysqluser, $mysqlpwd) or die("Connection not possible"); 
mysql_select_db($mysqldb, $connection) or die("Database select not possible"); 
echo "Ready without errors"; 
?>

Any Idea?

Regards Stefan