Cannot add a new owner to a Bank account

Dear Community,

I am having the following problem:

An ex-employee  is now an external supplier.
When I go to the Bank details of the employee supplier I want to add another owner (the new supplier record but it can be anyone) to this record and it gives this error message:

The external bank account already exists

One of the assignment of this bank account is related to operating unit.

Do you know any solution for this problem?

thanks,

Alex