Possible IE9/session variable issue?

[pfabrick]

We've been noticing a rash of complaints from customers about checking out using IE9. They're shopping as guests, go to the shopping cart and click "Checkout" (or use the Checkout tab at the top) and get a session error. We've gotten around this by having them login first (error doesn't happen if you're logged in). We're beating our heads against the wall here trying to figure out what's happening and any help would be greatly appreciated.

Here's what we have running:

ZC 1.3.7 (fresh install at that time) with Multi-Site, Wishlist, Google Analytics mods

Template customization of the Navigation tabs (js & css manipulation). No recent changes have been made to site (we're working on upgrading & a new template, but not on the production site).

Steps to reproduce problem (IE9 only): Add any product to cart, click on either "Shopping Cart" tab -> "Checkout" button OR "Checkout" tab. Error displayed "Whoops! Your session has expired."

http://onlinecatholicstore.com

Again, any help is appreciated.

[haredo]

Support for 137 is no longer provided on the forum.. Sorry...

Time to upgrade to 139h..