(1) Please excuse this clerical error.

(2) We tender you our apology for the inconvenience this error may have caused you.

(3) We request you to accept our regret for the error of our clerk.

(4) We greatly regret that we have caused you such an inconvenience.

(5) We wish to express our regret for the annoyance this mistake has caused you.

(6) We frankly admit we were at fault and we are anxious to repair the consequences.