Issue with orders from USA

[mdb44]

Hello,

I'm having issues with customers from the USA only. Eventhough all countries and states are active for PayOne, there is always "Invalid state. Please verify your data." at the payment validation. This error doesn't correspond to any listed error in Payone Docs.
Debug mode gives no lead...
Any idea where this may come from ?
Thanks a lot for your time.

This problem occures on PS 1.7.7.8 and also an old 1.6.1 version.