Web address in link causes errors (that are not of my making!)

From: Nigel Brown <nigel.brown@live.com> Date: Sat, 9 Feb 2013 21:02:02 +0000 Message-ID: <BLU0-SMTP10565369E781A20C8DB0DE382040@phx.gbl> To: <www-validator@w3.org> · This archive was generated by hypermail 2.3.1 : Monday, 18 March 2013 18:07:59 GMT

I have a line of code in the Sitemap on my web site at
http://www.nigelbrown.me.uk/my-sitemap.htm that gives rise to 2 validation
errors and 3 warnings. It is a link to a website (the Guestbook). But these
"errors" and "warnings" are not problems with my code; it is because the
validation does not like the Guestbook web address.

How can I help this?

Thank you.

Nigel Brown