Service Manager Process Error

Upon trying to invoke a WM Service from a Java Thread using doInvoke method of Service class [ resultData = Service.doInvoke(folderName, serviceName, mySession, threadData); ]

the below listed exception appears.

java.lang.NullPointerException
at com.wm.app.b2b.server.ServiceManager.processError(Compiled Code)
at com.wm.app.b2b.server.ServiceManager.invoke(Compiled Code)
at com.wm.app.b2b.server.ServiceManager.invoke(Compiled Code)
at com.wm.app.b2b.server.Service.doInvoke(Compiled Code)
at com.wm.app.b2b.server.Service.doInvoke(Compiled Code)
at com.met.srd.parallel.SRDThread.run(SRDThread.java:136)
at java.lang.Thread.run(Compiled Code)

Does anyone know why?