This may be related to (or the problem with) 1532 and some other tickets...

In IE7, the following line in jquery 1.1.4 is failing for me when I try to use easing. The problem seems to be with a negative value for z.now when the property (prop) is height (for example: prop='height' and z.now = -3.144324544).

So, essentially we are doing: elem.style.height = -3px

NOTE: the following line is from the z.a() function inside the fx() function:

y[prop] = parseInt(z.now) + "px";

Steps to reproduce...

Using http://jqueryjs.googlecode.com/files/jquery-1.1.4.js that is the 'lite' version of jQuery (I think) and the line number would be around 2372 or so

Note: I am using jQuery Easing v1.1.1 from http://gsgd.co.uk/sandbox/jquery.easing.php

1) set up animate() with the following, or similar (the critical part is having the easing argument), arguments:

$content.animate( {height:'toggle'}, {duration: 1000, easing: 'backinout'})

2) try to toggle against that, and the height (may) becomes negative, resulting in an 'illegal argument' in the IE7 browser. A negative height does not make too much sense, I guess. Essentially we are doing: elem.style.height = -3px

I have changed this code locally to circumvent the error (see below), but there are likely more situations that need to be handled by someone who knows the ins and outs better so that a more permanant solution can be found.

if(prop == "height" || prop == "width" ){
    y[prop] = Math.max(parseInt(z.now), 0) + "px";
} else {
    y[prop] = parseInt(z.now) + "px";
}