RSS trouble

<XML Parsing Error: undefined entity
Location: http://www.cycloblog.com/wordpress/wp-rss2.php
Line Number 17, Column 41: <title>Results of K-B-K; GP Lugano; Cl&aacute;sica de Almeira</title>
----------------------------------------^

In case the code doesn’t come out right, the little arrow is pointing to the G in GP. I can’t figure out what’s wrong. I’ve googled to no avail and checked that my xhtml is valid.

Any ideas?