New Post: Go to Checkout fails

I've chased this with DNN and they say there are some minor url issues when your using special chars in foreign language in IE9 and IE10, a fix being released for 7.1.2

I don't think this is the issue here, so either we've found some new issue with DNN or maybe there is a setup/corruption issue with your site? Although I can't think what!!

Have you tried recreating the issue on a new install?