During server startup, the server checks the Message Queue version. If the Message Queue version is incorrect, then the server upgrades using the imqjmsra.jar. This upgrade JAR and its classes will not be available to the server until the next restart. This situation only occurs if Message Queue is upgraded alone, or if Application Server is patched alone. A side effect of this situation is that sometimes server does not start.
Both Message Queue and Enterprise Server need to be maintained at the same patch level, or restart the server.