I found this on the website. This explains everything:

Argh. I foolishly forgot that I had set the expiration date on the latest version of MileTracker (0.9994b) to May 15. I also temporarily don't have access to the computer that I develop MileTracker on. Therefore I'm in a bind and I can't get the MileTracker install updated at the moment. I will get a MileTracker update out late on Thursday night or Friday morning that will resolve this issue, but until then if you need to run MileTracker, just set your computer's clock back to anytime before May 15, 2002. I truly apologize for the inconvenience.