utf-8 validation help

Validating http://www.toppingbooks.com/inline/ievents.html.

Hi,
First of all, thanks for such a useful tool!

I'm trying to convert my (not well written) HTML pages to XHTML and all the
other pages I validated all came out fine (
http://www.toppingbooks.com/home.html is one of them).

However, when I try to validate
http://www.toppingbooks.com/inline/ievents.html, it gives me this error
message:

Sorry, I am unable to validate this document because on line *24, 35, 46,
57, 68, 79, 89* it contained one or more bytes that I cannot interpret as
utf-8 (in other words, the bytes found are not valid values in the specified
Character Encoding). Please check both the content of the file and the
character encoding indication.

My question is:
What are the bits of (X)HTML in my code that the validator cannot interpret
as utf-8 and how can I chnage the code to enable the validator to interpret
it?

Thank you,
Hugh Topping