Don't for get to VALIDATE your pages using the W3C validator.
- You must use the Extended Interface, accessible from the link above
- You must use "iso-8859-1" for the Encoding.
- You must use "HTML 4.01 transitional" for the Type.
- You can see an example here
- COPY and PASTE the URL so you don't have typos
- The page must be online, or you must use the "upload file option"