Content-Length Header Issues

I wrote a program in C# that i deploy through my site here. It is built with an updater that downloads with a progress bar, showing the number of bytes, kilobytes, or megabytes downloaded, and the total file size. The total file size is not being retrieved because the WebClient cannot retrieve it from the Headers. A friend of min suspects it may be my webserver, because it does not work on any of my domains, in any directory. However, if I just change the URL to one on his site, it works perfect. Only my sites are problematic.
Box 5
Username: macsul