JavaScriptException with IE7

Hi

I am using Vaadin 6.8.3 and have a browser compatibility issue. My application works perfect in IE 8,9, Firefox an Chrome. But in IE 7 (and also in IE 8 quirks mode) I get a blank page and using the debug console, I get the following error:

JavaScriptException: (TypeError): Object expected number: -2146823281 description: Object expected

Any ideas what might cause this or is any component known to be not compatible with IE 7?