All the pages are fine- they all have /w/Page, except the Main Page.
The link when you first go in goes to /Main_Page (which is a 404) instead of /w/Main_Page (which is also a 404), and I can only get to it by going to /index.php?title=Main_Page (/w/Main_Page doesn't work).
However, any OTHER page works just fine and goes to the page if you put in /w/Page.
... I followed the directions completely and used shorturls.redwerks, so I don't know why the Main Page isn't working.