Changing the date on my web server stops my ASP.NET app from working

I'm trying to write some code that checks the number of days between two dates, when I set the date on my IIS7 server to anytime in the future I get the standard "Internet Explorer cannot display the webpage" screen. This happens if I comment out all my date checking code, with todays date it load开发者_开发知识库s with any future date it doesn't. I've tried rerunning IISReset which makes no difference.

Anyone seen this before?

Thanks Jamie

You've proven that you can retreive the current system date from the server. IMO, now you can go ahead and fudge the numbers by reading test dates from a file (override.txt, or whatever) and test your date calculation scenarios without having to mess with the server.
You will want to make sure that you have a common function for getting the system date, so that you can override in one spot. So if you're not already set to do that, re-tool the code a bit, re-test to ensure that you get the system date properly. Then drop in your override file and test away.