Sometimes, IE shows a "This page can't be displayed" error. This is IE's all-purpose "I'm sorry, I can't do that Dave" message. It can have multiple causes.
One cause I've seen more than once is an infinite redirect loop. This can be particularly difficult to recognize, if you have users trying to reproduce the problem, because they'll reload the page again and again, trying to produce the problem. That looks a whole lot like a redirect loop, reloading the page again and again.