Why am I receiving "could not enlist in transaction on entering meta-aware object" in my logs?

Issue

• I have a stateful session bean that is using two EntityManagers in the same method and I'm seeing the exception

  ERROR [JDBCExceptionReporter] Could not enlist in transaction on entering meta-aware object!; - nested throwable: (javax.transaction.SystemException: java.lang.Throwable: Unabled to enlist resource, see the previous warnings. tx=TransactionImple < ac, BasicAction: a0b324b:8f6:4b2f4e82:120 status: ActionStatus.ABORT_ONLY >); - nested throwable: (org.jboss.resource.JBossResourceException: Could not enlist in transaction on entering meta-aware object!; - nested throwable: (javax.transaction.SystemException: java.lang.Throwable: Unabled to enlist resource, see the previous warnings. tx=TransactionImple < ac, BasicAction: a0b324b:8f6:4b2f4e82:120 status: ActionStatus.ABORT_ONLY >))