Adsense-Deluxe plugin and xhtml error

I am getting the below message when I try to xhtml validate my page. I believe it is a result of the Adsense-Deluxe plugin, becasue when I deactivate the plugin I can xhtml validate my page. Can anyone tell me how to correct this or what it means?

“Sorry, I am unable to validate this document because on line 28 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. “

Thank you.