ASP.NET site that runs in Visual Studio 2012 will not run in Visual Studio 2013: mimeMap entry error

July 25, 2014 at 11:38 AMMadestro

I ran into the following error while trying to open a Visual Studio 2012 solution in the new version, Visual Studio 2013:

HTTP Error 500.19 - Internal Server Error

The requested page cannot be accessed because the related configuration data for the page is invalid.

The detailed information section listed the follwing config error:

"Cannot add duplicate collection entry of type 'mimeMap' with unique key attribute 'fileExtension' set to '.woff'"

The important thing here is not the mime type. It's the action of adding it that is causing the problem.

Apparently, the IISExpress version used by Visual Studio 2013 is based on newer IIS engines (7.0 and up) which throw this error when you add the same mime type at multiple levels in the config files.

You can obviously just add it at one level and solve the problem. However, more times than not this is not ideal and you still need to have the entry there.

Fortunately, there is a simple solution. Add a Remove directive right before you add the mime type:

      <remove fileExtension=".woff" />
      <mimeMap fileExtension=".woff" mimeType="application/x-font-woff" />
And that's all there is to it. By removing the entry right before you re-add it, you avoid this error.

Posted in: Visual Studio | Web Development