Page Cannot be Display/Document contains no data

I've had a weird error which I can't work out. I've been programming a page with a couple of Quickform forms on it and its been working fine, locally and on the production server. But now, for no discernable reason I cannot access that page (and only that page). In IE is produces the error: "The page cannot be displayed" and in Netscape it produces the error "Document contains no data". I should point out there is plenty of html on the page as well. Any ideas why I would get these errors suddenly for pages that were previously working, would be appreciated. Cheers Leonie