Apparently this is a known issue for some people and I found this article with instructions:
How to Enable Frames in Internet ExplorerErrors such as "Website cannot be displayed" are the bane of the internet surfer's existence. These types of errors can be caused by frames encoded into the website you're viewing. Internet Explorer 8 has the ability to display frames, but sometimes it just doesn't display properly. However, there are ways to get those pages to show up. Your security settings may be blocking the website's ability to display properly, or you can try changing your Compatibility View if the website used to work on an older version of Explorer.
Instructions
Adjust Security Setting
- Click on "Tools" in the menu bar that runs across the top of the program. Select "Internet Options" from the bottom of the drop-down menu that appears.
- Choose the "Security" tab in the options at the top of the box.
- Click the green check mark for "Trusted Sites," then click "Custom Level."
- Locate the option for "Navigate windows and frames across different domains," more than halfway down the list.
- Click the circle to "Enable" this option and click "OK." If you get a message that reads, "Warning! Are you sure you want to change the setting for this zone?" click "Yes," then click "OK" on the "Internet Options" box.
Hopefully that will work for you. However, the odd thing is that in my version of IE8 I checked and "Navigate windows and frames across different domains" is disabled, yet the forum displays perfectly fine. But then, what have I said about IE - there's no rhyme or reason when it comes to how it behaves for different people.