Java EE (Java Enterprise Edition) General Discussion

I'm running Tomcat 5.5.17. I've been working on an application for quite some time when the tomcat logs suddenly started to fill up with the following errors each time I restart Tomcat:

2006-09-29 21:15:10,539 | WARN | StandardSession.java | writeObject() | 1468 | Cannot serialize session attribute publicPictures for session 9184A48FEFC99FAA3573A4DE1F75CCD5

I've searched the web, and found out that the reason for this is that Tomcats "Restart Session Persistence" is turned on. So how do I turn that off?

According to a few sites in the web there should be a file called application.xml, in which I can put the line <Manager pathname=""/> to disable the Session Persistence manager. The problem is that on my Tomcat installation there's no such file.

So I tried to create the file $CATALINA_HOME/conf/application.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE application PUBLIC '-//Sun Microsystems, Inc.//DTD J2EE Application 1.3//EN'
		'http://java.sun.com/dtd/application_1_3.dtd'>

<application>
 <Manager pathname=""/>
</application>

But this had no effect at all. So can someone please explain to me how I can disable the Session Persistence manager?