Silverlight Error #2104 Could not download the silverlight application in IIS

You install a Silverlight Module to or DNN website and receive an error that shows:

ErrorCode: 2104
Message: 2104 An error has occurred

This error is advising that the IIS host server is not correctly configured for Microsoft Silverlight. The fix is easy, and something that a host service should be happy to do for you. This is because Microsoft Silverlight is becoming more popular, and no Silverlight applications will run unless the following changes are made. Notes from


Deploying Silverlight content to a production web server is a pretty easy process. Despite occasional misconception, Silverlight doesn't require a Microsoft-based web server: Apache can host up Silverlight content just as happily as IIS.

But there's one little gotcha: web servers are typically configured to only serve up a limited set of known file extensions as static content. That's all well and good, but Silverlight introduces two new file extensions (.xaml for loose XAML files and .xap for the zip-based binary packaging format). As a result, you need to add the MIME types for those file extensions to your web server so that it recognizes Silverlight content appropriately. Here are the MIME types you need to add to the server configuration:

Extension MIME Type
.xaml application/xaml+xml
.xap application/x-silverlight-app

That's all you have to do. Unfortunately, it's not possible to provide generic instructions for how to add MIME types, as it varies from server to server, but here are some links for various common web servers:

While you're updating the list of MIME types served, you might want to also add the relevant types to your web server to support WPF and ClickOnce applications. Here are the additional items you'll need:

Extension MIME Type
.manifest application/manifest
.application application/x-ms-application
.xbap application/x-ms-xbap
.deploy application/octet-stream
.xps application/

But what if you're hosting your Silverlight application on a shared hosting service and your hoster doesn't give you access to change these settings? The good news is that there are two options available to you. Obviously, you could take advantage of Silverlight Streaming, our free hosting service for up to 10GB of Silverlight content.

Alternatively, you can 'cheat' the web server by renaming the XAP file extension to a compatible MIME type. The XAP container is ZIP-based, so you can simply rename the output file from .xap to .zip and change the source param within the object tag contained in the HTML file to point to the new file location. Click on this hyperlink to see the technique in action - it's a plain HTML file that points to a ZIP file (containing the Silverlight content).

One last piece of good news: IIS 7, included in Windows Server 2008, already includes all the relevant MIME types for both WPF and Silverlight, including both .xap and .xaml extensions, so if you're using Windows Server 2008, you're all set. (The same applies to a clean install of Windows Vista SP1, although if you upgrade from the RTM to the SP1 release, your settings will remain unchanged until you uninstall and reinstall the IIS feature).

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