"Your session has expired" with Authorize.net SIM

[HDG]

After submitting an order, being taken to Authorize.net to enter CC info and hitting Submit I am taken back to my website which says:

Whoops! Your session has expired.
If you were placing an order, please login and your shopping cart will be restored. You may then go back to the checkout and complete your final purchases.

If you had completed an order and wish to review it, please go to your My Account page to view your order.

Any idea what is wrong? Thanks.

Database Host: localhost (127.0.0.1)
Server OS: Linux 2.6.18-53.1.4.el5 Database: MySQL 4.1.22-standard
Server Date: 06/20/2008 16:16:47 Database Date: 06/20/2008 16:16:47
Server Up Time: 16:16:47 up 27 days, 17:31, 1 user, load average: 2.08, 1.64, 1.63 HTTP Server: Apache/1.3.39 (Unix) mod_auth_passthrough/1.8 mod_log_bytes/1.2 mod_bwlimited/1.4 FrontPage/5.0.2.2635.SR1.2 mod_ssl/2.8.30 OpenSSL/0.9.8b PHP-CGI/0.1b
PHP Version: 4.4.7 (Zend: 1.3.0) PHP Safe Mode: Off
PHP File Uploads: On Max Size: 2M POST Max Size: 8M
Database Data Size: 632 kB Database Index Size: 422 kB

Zen Cart 1.3.8a
Database Patch Level: 1.3.8

[DrByte]

Is there a particular reason why your using SIM instead of AIM?
AIM is a more pleasant shopping experience, and isn't susceptible to the problem you describe.

[OregonBum]

Is there a particular reason why your using SIM instead of AIM?
AIM is a more pleasant shopping experience, and isn't susceptible to the problem you describe.

I'm having the same problem, & as of summer 2010 SIM is the only Authorizenet.net module I can use without having to go through PCI compliance.

I'm running the following:

Server OS: Linux 2.6.18-164.10.1.el5
PHP Version: 5.2.8 (Zend: 2.2.0)
Database: MySQL 5.0.91-community
Zen Cart 1.3.9d