Was there any final resolution? I am also having an empty cart issue.
I am using Cart66 with the following diagnostics configuration
Cart66 Version: 1.1.6
WP Version: 3.2.1
WPMU: False
PHP Version: 5.2.17
Session Save Path: /tmp
MySQL Version: 5.1.58
MySQL Mode: Normal
Table Prefix: wp_
Tables: All Tables Present
Everything works fine with firefox, chrome and safari (all installed on the same machine). But when I use IE 8 on windows 7 32bit I have the empty cart issue. On a different machine with IE8 on Windows 7 64bit it works fine. I turned on the debuging and this is what it reported.
[Cart66Session.php – line 209] Session is not valid – User agent changed
I have removed all cookies and cached files and even tried CammoKing’s suggested fix. Nothing has worked yet. Ideas?