Can't load different libraries on each cluster (Glassfish 3.1.2.2)

Hello,
I'm using GF 3.1.2.2 over Red Hat Enterprise Linux 6.3
I've several clusters and I need to load different libraries on each cluster.
I've read (http://docs.oracle.com/cd/E26576_01/doc.312/e24934/instances.htm) that the directory /config//lib is the folder where place "library files for all applications that are deployed to a specific cluster or standalone instance"

I've copied the jar files in this directory but applications doesn't find the classes.

Do I have to configure anything else?

Thank you