Hi Senthil,
As I wrote in the other thread (
https://groups.google.com/forum/#!topic/windowtester-pro/oK3wZr1xSWk),
without knowing your application, having a test snippet that reproduces the problem or at least seeing a screenshot, I can't help much.
You can try to call "new DebugHelper().printWidgets();"
before this error occurs, to see if the hierarchy of the widgets is correct.
Regards,
Fred