Thanks for your reply:
Which version are you using of the Extension? - ocmod v2.89
On which page is this issue? - Checkout page 2 step, when I put for example any working VAT code, it fills all details, but State/Region is empty and this prevents us from moving to next checkout step. (anyway, you can enable module and try to place order with VAT number, will be problem
)
Now module is disabled, you can try to enable it and will see the problem