There are two main points that you need to watch out for. The STATUS on the first line, should read 200 OK.
If your status code is 301 or 302, this indicates a redirection. Submission of these pages should be avoided as such pages may not be accepted by some search engines. Other codes, may indicate more serious problems.
Also important, is the content type. The Content-Type tag indicates the type of data which is returned when the page is requested. For HTML pages, this should be text/html.