During one of our release we started getting bellow error, while we tried to access our custom silverlight dashboard in MS CRM 2011. we were not getting this error in our development environment, it was comming only in production environment. when I tried to search about this error I found http://msdn.microsoft.com/en-us/library/ie/ee264315%28v=vs.85%29.aspx and I enabled below setting and it worked