I have the same problem with jboss AS5 (ver 5.0.0GA) and oracle XE. My Datasource <local-tx-datasource> <jndi-name>jdbc/TelemedicinaLocalDS</jndi-name> <connection-url>jdbc:oracle:thin:@localhost:1521:XE</connection-url> <driver-class>oracle.jdbc.driver.OracleDriver</driver-class> <user-name>kekekeke</user-name> kakakaka <min-pool-size>5</min-pool-size> <max-pool-size>50</max-pool-size> <!-- Checks the Oracle error codes and messages for fatal errors --> <exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.OracleExceptionSorter</exception-sorter-class-name> </local-tx-datasource> this error appears only first time in log, then never again and pool works properly. Any idea? thanks! View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4201861#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...