EJB application deployed on IBM Websphere application server fails to
invoke EJB after an idle period of about 30 mins.

WARNING: "IOP00710261: (INTERNAL) Number of invocations is already zero, but
another invocation has completed"
org.omg.CORBA.INTERNAL: vmcid: SUN minor code: 261 completed: Yes
       at com.sun.corba.se.impl.logging.ORBUtilSystemException.numInvocationsAlreadyZero (Unknown Source)
       at com.sun.corba.se.impl.logging.ORBUtilSystemException.numInvocationsAlreadyZero (Unknown Source)
       at com.sun.corba.se.impl.orb.ORBImpl.finishedDispatch(Unknown Source)
       at com.sun.corba.se.impl.orb.ORBImpl.releaseOrDecrementInvocationInfo(Unknown Source)
       at com.sun.corba.se.impl.protocol.CorbaClientDelegateImpl.releaseReply(Unknown Source)
       at org.omg.CORBA.portable.ObjectImpl._releaseReply(Unknown Source)
[...]