failed to load DefaultWidgetSet error alert in browser

I am getting the "failed to load widgetset (DefaultWidgetSet) error alert message while the application starts.I am using vaadin 6.6.5 jar and jboss6 app server and we are not using any widgetsets in our application.but the alert message is inconsistent(most of the time i am getting and not able to run the app.) .i have tried some solutions whatever has been specified in the forum.but still i am facing the issue.Find below the solutions i have tried.
1.Complete redeployment
2.Servlet mapping in web.xml(/VAADIN/*)
3.Removed the widgetset entries from the web.xml.
4.Extracted the widgetset from the vaadin jar and placed inside VAADIN folder of my webapp.

Could you please provide a solution how this can be solved?