I have to say, you should really submit a support ticket when you have something as critical as this.
I had a problem with credit cards in check out.
My last ticket had this response which I hope helps:
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We have conducted the investigation. While checking your site, we have found out that your credit card info page doesn't properly displayed in IE browser, however it looks ok in Firefox. So far, we can assume that it can cause the problems your customers mentioned.
We've uploaded the correct template from our default installation to fix the problem.
Hope, this will be helpful.
Please, let us know should the problem persists.
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As I use Firefox when working on my site I could never understand why my testing was always successful but customers often had problems - PayPal accounts were fine.
It is always worth subscribing to support services.
Chris