I am using a Windows Forms control in an Internet Explorer (IE) page. When IE downloads the control, it is distinguishing between upper- and lower-case letters in the web site URL. When I use the same site with different casing - such as http://111.1.1.1/WebSite and http://111.1.1.1/website - two copies of the control are download. Why is that?

It's simply a case that there are many examples of not being able to tell that two URLs are the same. E.g., your IP address URL and one with a domain name are two that are tough to tell for sure they're the same. One with different caps is the most trivial example, but there are many that aren't trivial.

Instead of trying to address them all, each URL ends up getting treated unique. If you reference the control in your HTML page with an absolute URL, it should eliminate the problem of users coming at your HTML page with different URLs.