System Error:communication problem after upgrading to vaadin 6.6.0

Recently , we have upgraded from 6.3.2 to 6.6.0 and I m getting “Communication Problem take note of any unsaved data, and click here to continue.” it is coming very frequently and also sometimes coming more than once. could you help me in this.

And this message is not coming in firefox 3.5. appearing in IE. tested in IE 7 & 8

Thanks in advace,
Sireesha M

Is it coming in the same places all the time? What do you do when it happens? Do you custom client side code in your application?

Have you recompiled/updated the widgetset in use?