Again Error: Coupon is either invalid, expired or reached its usage limit!

Please, I have this error when checkout = confirm:
Error: Coupon is either invalid, expired or reached its usage limit!

i tried everthing is about topic on forum.
some new idea?

is this happeningwhen you try to use a coupon? or does it always happen during checkout even when on coupon is used?

do you have coupon codes created?

have you made any modifications to any checkout files?

I'm experiencing this too. The strange thing is when I test this myself, the coupon works ok. But several customers complained that they got that error message (Error: Coupon is either invalid, expired or reached its usage limit!) when they tried to use the coupon. Is this a bug? I am still on 0.7.8 fyi