Unable to validate

When I tried to validate a document, I received this message:

I was not able to extract a character encoding labeling from any of the
valid sources for such information. Without encoding information it is
impossible to validate the document. The sources I tried are:

The HTTP Content-Type field.
The XML Declaration.
The HTML "META" element.
And I even tried to autodetect it using the algorithm defined in Appendix F
of the XML 1.0 Recommendation.

Since none of these sources yielded any usable information, I will not be
able to validate this document. Sorry. Please make sure you specify the
character encoding in use.

Does anyone know exactly what this means. I do have a DTD on the top of my
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

Received on Saturday, 31 May 2003 11:37:30 UTC