I have Slide-in working on www.tradereform.org and it works

I have Slide-in working on http://www.tradereform.org and it works fine. However, when active, it causes an error in the RSS feed so that no items display.

I ran a validate on http://www.tradereform.org/feed at w3.org, and here is the error message:

line 154, column 1: Undefined channel element: div [help]
<div id="wdsi-slide_in" style="display:none;" class="wdsi-slide wdsi-slide ...
^

line 168, column 238: XML parsing error: <unknown>:168:238: not well-formed (invalid token) [help]

... ss="validate" target="_blank" novalidate>

With Slide-in deactivated, RSS works. With activated, the error is always there.