Configure portlet Forum to use MySQL

Hi,

I've installed Jahia (4.0.4) on Windows 2000 with the default installer. So I used HSQL database. I've used Jahia to create somes pages. And I use the portlet Forum. Then I had to migrate to MySQL. After having changed the database, Jahia is working well but not the portlet Forum. It tries to use my old HSQL database. So I've changed the property file JAHIA_HOME\tomcat\webapps\Forum_myjahiasite\WEB-INF\etc\forum.properties .
 Here is the content of this file :

# Xo3 Forum Web Application Property's File

database.driver=org.gjt.mm.mysql.Driver
database.url=jdbc:mysql:///jahia
database.username=root
database.password=
database.maxConnections=10
database.initialConnections=10

(I used the default file for mysql)

But it doesn't work. Is there anything else to do to force the Forum portlet to use MySQL ?

Thanks
Olivier