Exception on starting dashbuilder on postgresql

There is an exception after defining/mapping a datasource (postgres) for dashbuilder. However the config looks correct. business central application was deployed without errors which used the same datasource configured on resource.properties.

20-Mar-2016 03:54:40.599 SEVERE [localhost-startStop-1] org.jboss.dashboard.annotation.StartableProcessor.wakeUpStartableBeans Error starting bean org.jboss.dashboard.database.hibernate.HibernateInitializer$Proxy$$$_WeldClientProxy
java.sql.SQLException: Cannot create JDBC driver of class 'org.postgresql.xa.PGXADataSource' for connect URL 'jdbc:postgresql://localhost:5432/jbpm'
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createConnectionFactory(BasicDataSource.java:2160)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createDataSource(BasicDataSource.java:2032)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:1532)
at org.jboss.dashboard.database.hibernate.HibernateInitializer.inferDatabaseName(HibernateInitializer.java:235)
at org.jboss.dashboard.database.hibernate.HibernateInitializer.inferDatabaseName(HibernateInitializer.java:222)
at org.jboss.dashboard.database.hibernate.HibernateInitializer.start(HibernateInitializer.java:123)
at org.jboss.dashboard.database.hibernate.HibernateInitializer$Proxy$$$WeldClientProxy.start(HibernateInitializer$Proxy$$$WeldClientProxy.java)
at org.jboss.dashboard.annotation.StartableProcessor.wakeUpStartableBeans(StartableProcessor.java:52)
at org.jboss.dashboard.Application.start(Application.java:74)
at org.jboss.dashboard.Application$Proxy$$$WeldClientProxy.start(Application$Proxy$$$_WeldClientProxy.java)
at org.jboss.dashboard.ui.controller.ControllerServlet.init(ControllerServlet.java:62)
at javax.servlet.GenericServlet.init(GenericServlet.java:158)
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1238)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1151)
at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1038)
at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4997)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5289)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1091)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1830)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassCastException: org.postgresql.xa.PGXADataSource cannot be cast to java.sql.Driver
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.createConnectionFactory(BasicDataSource.java:2149)
... 27 more

dashbuilder/META-INF/context.xml

WEB-INF/web.xml
META-INF/context.xml

dashbuilder/WEBINF/etc/hibernate.cfg.xml

java:comp/env/jdbc/jbpm

dashbuilder/WEB-INF/web.xml,

Dashboard Builder Datasource
jdbc/jbpm
javax.sql.DataSource
Container