Now What? (Validation)

I continue to try to get my site to validate, but now I get this error:

Result: Failed validation.
Sorry, I am unable to validate this document because on line 347 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.

According to Dreamweaver, this is line 347:

<a href="https://www.sassydevil.com" title="SassyDevil.com"> Return Home</a></div>

According to Editpad, this is line 347 (part of an affiliate code):

src="https://service.bfast.com/bfast/serve?bfmid=2181&sourceid=41462166&categ

and it’s part of this (lines 343-348):

<li><a href="https://service.bfast.com/bfast/click?bfmid=2181&sourceid=41462166&categoryid=rn_home" target="_top">Barnes & Noble.com</a>
<img src="https://service.bfast.com/bfast/serve?bfmid=2181&sourceid=41462166&categoryid=rn_home" border="0" width="1" height="1" nosave ></li>

Can anyone tell me what character(s) is affecting the validation? Thanks.

And, it’s kind of unrelated-yet-related, but should I change my doctype to an HTML doctype, or is XHTML required for WordPress?