Thanks for the response. I have been investigating further and I figured out that it was passing the CSS.
I have cut down the CSS to just a couple of classes and it seemed to work.
Is there an easy way for me to debug which CSS makes it fail?

I have spotted one, FILTER statement for IE.

Is there issues like browser specific styles used for progressive enhancements:

-webkit-box-shadow: 4px 4px 3px #888;