"Error creating managed object for class org.jboss.weld.servlet.WeldListener"

Following the Arun Gupta's Java EE 6 Hands-on Lab using Netbeans 7.0.1 and Glassfish 3.1.1, I found the following error, which prevented me from deploy the app: Error creating managed object for class org.jboss.weld.servlet.WeldListener.

I just restarted Glassfish, did a Clean and Build and the problem was gone :P

The Lab is a very good way to know several new cool Java EE 6 features.