Flash config files and MIME types

I ran into this situation for the first time today. A client had purchased a Flash application and couldn't get it to work correctly. The company they bought it from said that the configuration file wasn't getting loaded correctly, but couldn't provide any further guidance. The tech support rep couldn't provide a location of the config file or any details about how it was being loaded. Since the technical support was so lacking and I had no intention to steal their code, I figured that the only thing I could do was take a peek inside the SWF. I used Flare to decompile the Actionscript from the SWF and started looking to see how they were loading the configuration. First this tidbit:

function loadConfig() {
var v4 = new LoadVars();
v4.onLoad = function (success) {
....
};

v4.load(_url + '.cfg');
}

Hmm... So they were using the builtin LoadVars.load() method to retrieve the config file from a URL that ended in ".cfg" Looking a bit further, it turns out that the _url variable was defined as follows:

this._url = xmlx.config.requestURL;

So they're trying to load a file with the same url as the SWF file with a .cfg appended to the end of it. Punching that address into a browser gave a 404 error. After checking to make sure that the permissions were okay and that other files from that directory were accessible, I took a look at the MIME types. This was an IIS server and by default IIS doesn't serve up content without a defined MIME type. As soon as I added ".cfg" as "text/plain" and restarted IIS, everything worked fine.