Did you check the group and owner of the folder "/var/lib/geoserver/geonode-data" ?
We found that if you create/copy the folder from another installation usually the owner and the group is not set correctly to "tomcat6" and geoserver is not able to read that folder so set the default data directory to "/var/lib/tomcat6/webapps/geoserver/data". Ciao, Thomas
