I found this on a previous issue and think it may be connected.
Posted By: firstname.lastname@example.org (Ray Borduin) Message 10 in Log
Date: 03/29/2012 09:45 pm No Attachments
Title: RE: Will not accept captcha code
The issue on this site was that you had a php.ini file in the directory with the contact.php page that changed the way session variables were stored and that php.ini file was not in the WA_ValidationToolkit directory so they weren't sharing the same session data.
I copied the php.ini file into the WA_ValidationToolkit directory and that seems to have resolved this issue.
I have include the file (page) that is causing the issue with Internet Explorer and a page that is working fine. To recreate go to gift_certificates.php. Thank you.