TOPIC: Checkout issue DT_MAXIMUM_CART_WARNING_FRONT 0 DT_MAXIMUM_CA

Hi I'm having issues with the checkout function on my site. Once the registration form has been filled out and the confirmation page has been accepted I get the following error message
DT_MAXIMUM_CART_WARNING_FRONT 0 DT_MAXIMUM_CART_WARNING_BACK

And it will not let me go to the checkout PayPal stage.

submitted a ticket 3 days ago but nobody has bothered to get back to me. If this was for a personal site and a free extension that wouldn't be a problem, however my client has paid for this extension and wants their site to be able to work properly. A little support would go a long way please.