Error in Silverlight application code: 2104 Could not download the Silverlight application. Check web server settings

Setting up a Silverlight application for the first time I got a JavaScript error of "Unhandled Error in Silverlight Application Code: 2104" with an accompanying message "Could not download the Silverlight application. Check web server settings"

Being new to this and largely just experimenting with Silverlight for the first time wasn't 100% what to do. At least it pointed me in the right direction with its "Check web server settings" comment at the end.

I checked the MIME types for my site. Sure enough there was no mention of the .xap extension. Yes, that would be the problem.

Solution

I added a MIME type with extension ".xap" and MIME type of "application/x-silverlight-app" and it all worked pleasantly.

I thought this was a bit weird that it didn't come pre-registered but oh well, hope you find this useful.