Site Error Only On Vista And IE?

So I have this client who has a web form, the form was not made by me, I am debugging it as it has error's it seems. He has had 3 clients in the past two days complain they cannot finish the form, when they get to step 2 and click the button to go from step 2 to 3 they get this error:

Type Error: Unable to get value of the property (error): Object is null and undefined.

Now to me that looks to be JS, but there is no way at all to replicate it! I have tried this same procedure in IE6(XP), IE8(XP), Chrome, FF and it never happens to me ever.

I am pretty sure it's JS related since the form is never reloaded for each page, it's a JS tab paging system for each step.

Now he did finally get answer's from two of the 3 that had problems. They only said they were using IE on Windows Vista. And user's are not the most techie so I have been trying for two days to get info from them and nothing, info like IE version and what toolbar's and plugins they might have installed. Nothing.

So I am left here at this point. Does anyone know of anything related in Vista?

I don't have Vista so I cannot test this. I am testing right now on 7 with IE8 and then upgrading it to IE9 to test on 7 with IE9.

The site is here: [URL]

It's on step two, you get to step 2 by finishing step 1 and clicking on "Complete Application" to go to step 2. It's when clicking on the button to continue from step 2 to 3 that it happens.

As I said I cannot seem to duplicate this in any way.

I was hoping someone had Vista and IE to test for me, since your a coder you can screenshot for me the error and what happens, maybe that will help ha ha

Or maybe this has happened to someone before, the form seems to be using Dojo as it's FW.