I.E. 9 trouble

if you go to:
https://www.tncsg.org/classes/

then choose a class:
then click I'm attending

You are then prompted to login or register
If you choose to register when using internet explorer 9 the registration process hangs up. The user also does not have the next step available to them...paying for the class.

This process is working in firefox and chrome.

I was thinking maybe it's a javascript incompatibility issue.

Any thoughts?