orders with free items wont get through

hi there my clients site seems to have an issue with your plugin.
whenever activated the rules for 1 free item if you buy 5 or 11 or 23 does not seem to react porperly to the ordering process.
it will throw a free bottle of wine to the cart, but you can’t check out to paypal or othe paying systems.
you get an message “contact support” – for all items without discounts it works well with no issue.

how can we solve this quickly?
all my best
telemarker

The page I need help with: [log in to see the link]