I dont see anything obvious in the site that would cause the transaction to fail using IE.
Can you reproduce the failure?
If you can reproduce the failure I could start an incident so we can investigate the issue with you, but in order to troubleshoot, we need to be able to reproduce the problem. It's impossible to find the cause of a problem that cannot be reproduced.
it could be an IE Security issue causing the checkout failure, here are a few additional things to try:
-Clear the browsers cache and delete any saved cookies.
-In IE, click the Tools menu (Icon of a gear in the top right corner) and select Internet Options. On the Privacy tab, click the Advanced button, Check the "Override automatic cookie handling" box, and check the "Always Allow session cookies" box.
- Still on the Privacy tab, click the sites button, have them add your domain to the always allow list
- On the security tab, select Trusted Sites, then click the Sites button and add your domain to the Trusted Sites list. Select restricted sites, and make sure your domain is not on the restricted sites list.