v150 Pay by invoice; Invoice Payment Module for v1.3

Decided to start a new thread :)
Hi

This worked fine until this week; last time I was sure it worked OK was last Friday (12th July) when a customer paid by invoice.

Problem is when I am in the shopping cart & click on checkout then it just brings up the shopping cart page again (no error message); I tried "opening in a new tab" & I get the shopping cart page again. I have 2 languages English & German; same problem in both.
I have a Paypal button & that works OK.

I checked the error logs; nothing logged.

I re-installed the "Pay by invoice" & also re-installed the "checkout_shipping.php" from back up.

I am using v1.5.1 standard template with the following add-ons
Quantities by option
German language
Pay by invoice

I checked all the folders & I have added/changed nothing since Friday; maybe I configured something - there is no log of config changes?

BTW here is the link shown in the checkout button "href="http://www.simmar.ch/catalog/index.php?main_page=checkout_shipping""

It is just a link or is there some checking somewhere that could stop the page displaying?

Please close this thread; I found a problem in my options which caused the "empty cart" question to click in :(