Error The amount to be charged is zero

I'm running 1.5.6.4 version and everything is working fine, except for this error. I recently activated a Coupon for 40% discount on all items until May 31. The coupon discount works and calculate fine, subtotal, tax and everything is fine until you click on the last step to make payment.
this is the last step image:


and when you hit the continue button, shows this:



Any clue on that? I tryed changing order of the coupon, subtotal, tax, shipping and totals but doesn't works
Thank you

Update: I found this: The error remain when i use Paypal Express checkout option; i activated Paypal Standard payment option and works fine, so for the moment i suspend Paypal Express as a payment method in my site. I must say the payment method works great if you don't use a coupon.

If you have a solution please share!

jaguar9 wrote:Update: I found this: The error remain when i use Paypal Express checkout option; i activated Paypal Standard payment option and works fine, so for the moment i suspend Paypal Express as a payment method in my site. I must say the payment method works great if you don't use a coupon.

If you have a solution please share!

Hi Jaguar thanks for updating because I just noticed the same thing with Paypal express and this error. Do you know what can be done to fix this so people can use a coupon with Paypal express?