I have searched high and low for a solution, and I'm desperate. Any help will be greatly appreciated!

ZC v1.3.8a
Cybersource module v1.04 (great contribution by deBeaujeu!).

The order is getting through to Cybersource fine, but on the return, it always gives the "Whoops, your session has expired" and the order is not recorded in ZC.

I know this problem has been logged before. I've been through the forum and the very detailed implementation guidelines. These are the measures I've already taken:

- module files installed (4) and checked settings
- submitting to 'https://orderpage.ic3.com/hop/ProcessOrder.do'
- obtained new HOP file

- double-checked module settings in ZC admin
- installed and active
- set to "production" mode
- database content seems correct

- SSL is dedicated (one domain, not several)
- also verified with Comodo Vengine
- SSL enabled (true) for catalog and admin

- checked Cybersource settings
- return receipt url and box checked
- decline receipt url and box checked

- reviewed the following forum posts (and others):
- http://www.zen-cart.com/forum/showth...505#post337505
- http://www.zen-cart.com/forum/showth...ght=shared+SSL


Also reviewed posts on general time-out issues and changed the following:
- set cURL proxy to 'false' (using GoDaddy)
- tried disabling SSL, no effect

I don't know if the issue is with ZC, Cybersource, GoDaddy or me!
Help! please and thanks.