There is a "Can't Open Connection" because there is an XA exception. And the XA exception is raised because the xa-datasource isn't supported, at least with MySQL Connector/J 5.0.7, MySQL Cluster Server Pro 5.1.39, on a Linux kernel 2.6.18-164.el5. Replacing the xa-datasource with a local one solves the problem. So, at least for this configuration, the jBPM 4.4 installer (ant install.jbpm.into.jboss) incorrectly creates the jbpm-mysql-ds.xml file to use xa datasources. This file has to be modified manually, as a post-install operation, such that to replace the xa-datasource element by a local-tx-datasource one, in order to get the product working.