Posts on home page and archives..but not in single view.

Hi,

I am having a problem with Singe Posts Displaying. They yield a 404 error.

– If you click on the home page (its a Gay Travel Guide, so no porn or anything dodgy)…

http://www.gaysitgesguide.com/serendipity/

(all posts show up fine)

If you scroll down take any post (eg, the death of the Carnival King).
http://gaysitgesguide.com/serendipity/2009/02/26/the-death-of-the-carnival-king-2009/

Even though it shows in the list view, I get a 404 error when the individual post is requested directly.

Any advice or assistance appreciated.

K