could not load type 'system.data.entity.design.aspnet.entitydesignerbuildprovider'

Question

<add extension=".edmx" type="System.Data.Entity.Design.AspNet.EntityDesignerBuildProvider" />

this is the Assembly of my System Web.config file

Answer 1

Open your web.config and add this line below in the Assemblies section:

<add assembly="System.Data.Entity.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />

For more information, check this link:

http://forums.asp.net/t/1698282.aspx

Hope this helps

Answer 2

Adding to @wandos answer, here is the layout for web.config:

  <system.web>
    <compilation debug="true" targetFramework="4.5">
      <assemblies>
        <add assembly="System.Data.Entity.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
      </assemblies>
    </compilation>
    <httpRuntime targetFramework="4.5" />
  </system.web>