I am having the exact same problem. The charge actually goes through the viaklix system but zencart comes back with this error:

Login Time Out
We're sorry but for your protection, due to the long delay while either checking out, or on a secure page, the session has timed out.

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, or had a download and wish to retrieve it, please go to your My Account page to view your order.

And zencart does not recognize that an order has been placed.

Any help PLEASE!