Got an IllegalStateException: unread block data while Querying on WTPart

Hi All,

I need to export all WTparts from Windchill DB, so i used below code, it previously works but it suddenly gives an such errors,, i also observerd that it related to only WTPart.. any query on WTPart is not Working.. each query gives same error: java.lang.IllegalStateException: unread block data

my Query is here..

QuerySpec qs = new QuerySpec(WTPart.class);

      QueryResult qr = PersistenceHelper.manager.find(qs);

      while (qr.hasMoreElements()) {

        prt = (WTPart)qr.nextElement();

        cName = prt.getContainerName();

        partNum = prt.getNumber();

system.out.println("*******" +partNum);

}

Exception in thread "main" java.lang.IllegalStateException: unread block data

    at java.io.ObjectInputStream$BlockDataInputStream.setBlockDataMode(ObjectInputStream.java:2419)

    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1380)

    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)

    at wt.method.MethodResult.readExternal(MethodResult.java:152)

    at java.io.ObjectInputStream.readExternalData(ObjectInputStream.java:1835)

    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1794)

    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)

    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)

    at sun.rmi.server.UnicastRef.unmarshalValue(UnicastRef.java:324)

    at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:173)

    at wt.method.MethodServerImpl_Stub.invoke(Unknown Source)

    at wt.method.RemoteMethodServer.invoke(RemoteMethodServer.java:647)

    at wt.services.ServiceFactory$ClientInvocationHandler.invoke(ServiceFactory.java:349)

    at com.sun.proxy.$Proxy0.find(Unknown Source)

    at ext.util.WindVUtil.getLatestParts(WindVUtil.java:690)

    at ext.util.ExportParts.exportParts(ExportParts.java:125)

    at ext.util.ExportParts.main(ExportParts.java:101)