IE issues

IE issues

Hi,

It's probably caused by scripts written by us, and some of the old prototype scripts we're migrating to jQuery still, but we're having some major issues with Internet Explorer (don't we all do?)

First off, we're getting an error
on jquery.js, line 5899 - invali argument (currently using 1.4.2 from Google CDN).

The line reads:
fx.elem.style[ fx.prop ] = (fx.prop === "width" || fx.prop === "height" ? Math.max(0, fx.now) : fx.now) + fx.unit;

Does anybody have an idea what might be causing this?

Secondly, jqGrid is not working at all under IE.

I have no clue as to how we can debug stuff like this in IE. We use firebug while developing, and we should have been testing more thoroughly on IE during development, but I'm a little stuck now in terms of patching these issues.
How can we debug the code in IE?

David.