Unfortunately I'm stuck supporting IE6 as it's an internal app.
I can't seem to reproduce creating a simple test page. I wonder if it's down to the shear size of the page and IE6's crummy JavaScript support. The page where the error happens contains a very large and complex SVG based image editing embed (hence I can't even test in FF or Chrome).
Once loaded there's 2MB worth of JavaScript and 10MB+ of SVG loaded. I could be hitting some limit somewhere that stops jQuery being able to reliably query the dom.
I guess for now I'll have to stick with the Try/Catch block until I can convince the business to get the staff onto a more recent browser with better JavaScript debugging tools.