The form works perfect in Chrome and Firefox but gets hung up at different stages in the submission process, anywhere from 25% to 82% complete, a few times it made it to submit but then would not submit.
I have done the following to check for conflicts:
1. Disabled all plugins (they are still disabled)
2. Tested on Twenty Twelve, Twenty Eleven and Twenty Ten themes, the same problem appeared.
3. I have disabled Output HTML5 in the settings panel.
Thanks for your help.