Someone asked how to use asp:Silverlight control in Silverlight forum. He said that he is getting the error above after adding asp:Silverlight control to ASP.NET project where he host Silverlight content.

Error Screenshot

Solution :

Remove this <system.web><compilation debug=”false”><assemblies>

<add assembly=”System.Web.Extensions, Version=3.6.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35″/>

It’s because you have added two different version of System.Web.Extension in your project. The one that you have is 3.5.0.0 but when you place asp:Silverlight control in ASP.NET, the new version (3.6.0.0) will be added in web.config. So, you have to remove this lin.

Happy Silverlighting! :)