-//W3C//DTD HTML 4.01 Strict //EN ERROR

how do I get rid of this error


the "grubby" page is
http://www.dubdubdub.net.nz/acc/tactile_paving.html

at the w3c validator page
https://validator.w3.org/check?uri=http%3A%2F%2Fwww.dubdubdub.net.nz%2Facc%2Ftactile_paving.html&charset=%28detect+automatically%29&doctype=Inline&ss=1&outline=1&group=0&st=1&user-agent=W3C_Validator%2F1.3+http%3A%2F%2Fvalidator.w3.org%2Fservices

it says
"the Document Type (-//W3C//DTD HTML 4.01 Strict //EN) is not in the
validator's catalog"


I am thinking if (-//W3C//DTD HTML 4.01 Strict //EN is not in their catalog
then why are they suggestion it could be used ?


>From Eric
Footnote: it was a tidy website until all my wireless data got eaten up by
obese websites.