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Unzip WSO2 ESB distribution to a place of your choice. And then remove the geronimo-jta_1.1_spec-1.1.0.wso2v1.jar ( This JAR file can be found in $ESB_HOME/repository/components/plugins). The reason is using of the implementation of javax.transaction.UserTransaction6 of JTA provider (here JBoss) and if we have both in class path, there is a classloading issue which causes the transaction mediator not to work.
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