"Page Not Found" for Posts

I have written a post (only one, everything else so far is a page). I have given it a catagory (event). The post contains a slideshow. But when I try and view the post it I get an error message, “Page Not Found.” If I go to the catagories on my menu and it event it shows up on the event catagory page. When I select the post from that screen, same message, page not found.

I am using permalinks /%pagename%