Sorry, didn't realize that it was your site.
An I don't know ASP. So I am not much help there.
If it wee me, I would try dome different things. But not mess up my main site. Likely you have enough web space that you can make another web folder where you can experiment with things.
For example:
If
www.mydomain.com is my main page, then I would create a fold called
test_only that most users would never try. I would pull it up as:
www.mydomain.com/test_only and make a bookmark to it.
Next I would take bits and pieces of the code from the main page and test each element until I find the place where IE8 shows an error.
Also, you should be able to duplicate the problem using your own computer as a local web server.