Problem with '+', '-' & 'x' buttons in cart summary.

[Rigs]

Hi, I'm having a problem where once I have a product in my cart and I'm looking at the cart summary, if I try to add, subtract or delete the product using the buttons +,- or x, I get redirected to an error page telling me that the page is not available.

Some things to note:

- I am using SSL and want to continue to.
- This problem only seems to occur when the name & address details have been entered.
- The page in the address bar that it wants to go to is

cart.php?add&id_product=13&ipa=0&token=68a325b4101236d0677f604f9aac1f35

which then tries to go to

fastlane.php?step=1

-As you may have guessed from the above, I am running the fastlane checkout module for 1 page checkout.

Now, I have asked the module creators who have told me it's a theme issue as the theme is based on 1.2.x and needs to be updated. I asked the theme guys and they have said it's a prestashop thing as it is looking to go to cart.php (both have been really helpful by the way).

So here I am asking the question! FYI I'm running version 1.3.2.3

Edit: I forgot to mention that when the error page is up you can still see that the cart has been updated (according to whichever button you have pressed) in the cart block at the top of the screen.

Any help would be HUGELY appreciated as it's driving me mad trying to work out where the problem lies.

Thanks.