I had the same problem I deleted the server from the server tab, and also the server folder under your eclipse workspace, restarted eclipse, set up a new server, and it appears to be running OK now.
Quick update, I ran a certain
jsp, which seemed to screw everything up and give me the same problem, this time around I just right clicked on the server and deleted it, and checked 'Delete unused server configuration(s)' - that seemed to do the trick.
UPDATE - I think I know why I got this problem, I had made a small error in my WEB-INF/web.xml file, once I corrected this, it worked fine.