Have you updated to 4.03 and installed a web-application you developed under 3.x? I had the same error when I did so. The root cause was that the parser under 3.2 was not validating, the parser under 4.03 is validating. So my web.xml under 3.2 worked but was not valid for the DTD (I never checked it). I had to repair my web.xml until it was valid (esp. be carefull with the doctype declaration).
Greetings, Hans
