My b2evolution Version: 2.4.5

I try to keep my blog standards-compliant. I upgraded yesterday but I've now got one error picked up by [url=http://validator.w3.org/check?uri=http%3A%2F%2Fgeekblog.oneandoneis2.org]the W3C checker[/url] that I can't work out how to fix.

It's complaining about one of the divs in the sidebar search:

<div class="search_options"><div class="search_option">

Any suggestions as to what I need to do to get rid of this one last error?