"The Content-Type header is sent by your web server (or web browser if you use the file upload interface) and depends on its configuration. Commonly, web servers will have a mapping of filename extensions (such as ".html") to MIME Content-Type values (such as text/html)."
I then randomly checked a number of my previously checked HTML pages and received the error for all of them. I have no idea what the problem is. Any insight will be welcome. (NOTE: When I check the same pages from their URL they check out fine.) Thanks much,