voucher problem: bying for a smaller amount then set on the voucher not possible?

[vermiljoenshop]

I 'm trying to test the vouchers I'm creating, but there seem te be a problem.

I create a -50€ voucher discount on order amount, 1 voucher, to be used 10 times (I want to give the client the chance to use the amount in different purchases)
When I test and make a puchase of 20€, everything goes well untill the moment of paying. This failure notice appears:
Fatal error (Discount -> quantity_per_user = 10.00)

I tried changing the times possible to use the voucher to 1 to zero... nothing seems te matter and solve the problem.

Ideal would be that, after a purchase of 20€, the amount of the voucher is set to 30€, and that the purchase is assumed to be paid. But now, nor the client nor me receives a mail about the order, because the order failed.

What am I doing wrong in setting the voucher, or is it simply not possible?

Thanks for helping me out!

Vermiljoen