Hi,
This is an error message which usually displays when the current user is saving his address but the VAT number provided in his address doesn't correspond to the country selected in that same address and only if the "VAT number check" setting of the HikaShop configuration page is turned on.
So I would recommend going to the Customers menu, looking for your user entry there, and checking the addresses set in it. One of them must have a VAT number which doesn't correspond to the country selected.