Appearance > Widget admin page stops loading

On a site I administer, they have the latest version of Custom Sidebars Pro, When they go to Appearance > Widgets, the page starts to load, then stops loading before the available widgets gets finished. If I go to view the source, the code stops rendering at

<label for="widget-links-__i__-limit">Number of links to show:</label>
<input id="widget-links-__i__-limit" name="widget-links[__i__][limit]" type="text" value="" size="3" />
<div class="csb-clone csb-clone-links-__i__">
<input type="hidden" name="csb-clone-button" value="0" />
<input type="hidden" name="csb_clone[group]" class="csb-clone-group" value="11" />
<input type="hidden" name="csb_clone[state]" class="csb-clone-state" value="new" />



When I turn off this plugin, everything renders fine without any problems. Any ideas on what is causing this to happen?