Message "enter bank control key" while inserting new vendor via transaction XK01..

Hello,

I have created many new vendors in SAP via XK01 but yesterday when I tried to insert new vendor (which is from Spain) and define bank details I received this message "enter bank control key" I am not sure what to do, where to enter this bank control key because I din't have to do this before..

Any help is appreciated and many thanks in advance for prompt replies.
Sam