Manage file extensions served by a web server

If your web site exposes files for users to open, and certain file types open and certain file types don't, then you will need to add the extensions that aren't working to the MIME Types associated with the site in IIS.

1. Open up IIS
2. Select the Site, and choose MIME Types in the IIS section.
3. Click on Add, and add the extension.

A quick google search should obtain the MIME Type for the extension you want to add.