Silverlight Error Messages : Could not download the Silverlight Application

When deploying a Silverlight application on IIS you may get a script error: 'Could
not download the Silverlight application'. The cause of this problem is that IIS cannot understand the xap object and it is considered an unknown extesion.

IIS won’t let you access those files on the server. When you installing the Silverlight SDK on your development computer the mime type is installed on your IIS, yet servers without that SDK or the latest version and service packs won’t know about xap.

The solution for this problem is pretty easy.
All what you need to do is to add the MIME type to website properties for .XAP File type(it is application/x-silverlight-app).

So, in MIME Add new :
File name extension : .xap
MIME type : application/x-silverlight-app

Hope it helps all of you,

Happy coding