No, you may not. An error does not give you the right to the money: you would only have the right to it if it was deposited to your account pursuant to a contract, as settlement of a claim, for work done or services rendered or goods sold, as an inheritance, or as a deliberate gift to you...i.e. it was intended for you, for some reason. But if just showed up by accident, it is not yours, anymore than someone could, for example, keep your laptop if you happened to have accidentally dropped it on their lawn. Yes, if no one ever comes forward to claim it, it may, as a practical matter become yours; and after several years have passed and any applicable statutes of limitations have expired so you could no longer be sued, if necessary, to get the money back, it will then--and only then--become yours legally. But if at any point in the next few years, the rightful owner comes forward, you must return it; if you do not, you could not only be sued, but would potentially be guilty of theft, for knowingly attempting to take something which you know is not yours.