So you also have to add the Mapping Handler, and for that you have to have the Windows Feature called Classic Asp installed in order to handle the mapping. The MIME type enables the file extension on the server and the Mapping Handler tells IIS what to do with it. These folks are all correct to say you need to add the MIME type. I had this problem too - and the problem turned out to be file permissions on the folder where the json file was stored. (or just the detailed errors on the local console).

404 3) to determine exactly why your website isn't serving content for IIS 6, or If you're experiencing this sort of problem, open up the website's web log files, and have a look at the sub-status code (i.e. aspx files generate a 404, you probably don't have ASP.Net installed) if you're getting a 404 on an active content type in IIS 7, it may also mean your handler is not installed - so you need to actually go install the component that supports that file extension (for example, if.Active content files served by any extension must have that extension allowed in the Web Service Extensions restriction list (aka ISAPI/CGI restrictions in IIS 7).

this means that IIS treats them as active content, not static files.

Unless a script handler (active content engine, eg, ASP/ASPX/PHP/Java/ISAPI/etc) is associated with them.

See: IIS 6.0 will not serve unknown MIME types.

IIS won't serve files that don't have a MIME type associated with them.

To consolidate answers into one more general answer:

Go to iis web server extensions