Silverlight Grid Error CRM 2013 online -Cannot perform runtime binding on a null reference

Hi,

Our customer has got an online trial instance for CRM 2013 set up. we had built a Silverlight Grid for revenue forecasting purpose on opportunity entity form last year, which was working fine in CRM 2011 but since 2013 they are experiencing following error on opportunity form load:

CrmScriptErrorReport>
  <ReportVersion>1.0</ReportVersion>
  <ScriptErrorDetails>
   <Message>Unhandled Error in Silverlight Application Cannot perform runtime binding on a null reference   at CallSite.Target(Closure , CallSite , Object )

 ScriptObject xrm = (ScriptObject)HtmlPage.Window.GetProperty("Xrm");
            ScriptObject page = (ScriptObject)xrm.GetProperty("Page");
            dynamic dynamicPage = page;

            dynamic _startDate = dynamicPage.data.entity.attributes.get(ServerUtility.GetStartDateFieldName()).getValue();

If I clear the browser cache I get rid of error but then we loose any changed data on form. We are using IE 10. we have also tried the same on IE 8 but same problem happens.

Interestingly when I put alert before retrieving CRM field value, the problem of dynamicPage being  null disappears but then the annoying thing is user has to click ok every time form loads/refreshes.

we have also raised with issue with Microsoft and they have assigned an escalation Engineer but so far no luck!

Any ideas please?

Thanks

Umer