Webservice invocation is failing in clustered environment


I have a service containing pub.monitor.process.instance:getInstanceList and the service is exposed as webservice. When I invoke the webservice in dev (non cluster), it is working fine and returning instance list. When the same webservice invoked in QA (clustered with 2 node), it is not returning instance list. I tried with both cluster cache enabled and disabled status without any success. we are using 8.2 sp1.

Any idea.

Thank you for your time