Could not enlist in transaction on entering meta-aware object!

This errormessage provided by the Jboss j2ee server gave me a major headance. In a project we are using 2 datasources:

• an oracle datasource being used by iBatis DAO layer
• a postgresql datasource being used by JPA DAO layer

After invoking both DAO layers I got this nice SystemException by the JTA transactionmanager.

Investigation showed me ( a few hours later ) that the oracle datasource is not XA by default. You have to configure it to use the XADataSource. You can find a example in the jboss distribution in docs/examples/jca/oracle-xa-ds.xml