WebSphere Application Server has shipped with JAR files for the WebSphere MQ JMS provider since Version 5.0 as they were, at the time, required for the embedded messaging provider. However, if those JAR files do not match the version of WebSphere MQ you are using (as is the case with WebSphere Application Server V6.0 and WebSphere MQ V6) you may see error messages such as java.lang.NoSuchFieldError: msgToken. As documented on the support site and in the InfoCenter, on the server-side the correct thing to do is update the MQ_INSTALL_ROOT WebSphere variable to point to your real WebSphere MQ installation. What I haven’t seen documented anywhere is what to do in the case where you are using the WebSphere Application Server client container. In that scenario, you need to modify the JMS_PATH environment variable defined in the launchClient batch file in the application server bin directory.