IE-only error related to custom animation

IE-only error related to custom animation

There is a plugin I am developing for a menu that stretches to match the height of the parent node. During the animation call, in IE7, I get the following error: "Line: 5899 [of jQuery.js]; Error: Invalid argument." The plugin works as intended in Firefox and Chrome.

http://nathanbaker.awardspace.biz/

What gives?