Hi Stefano,
sorry I didn't mean you have to patch 4.5, I was just wondering if you did change something since the error "property mapping has wrong number of columns" seems to indicate that there is a mismatch between the mapping and the class. I don't see any error if I build from source and execute the testsuite with
svn co http://anonsvn.jboss.org/repos/jbpm/jbpm4/trunk jbpm4
mvn clean install