APOLOGY FOR RETURNED CHECK: BANK ERROR, REPLACEMENT ENCLOSED
You can understand my embarrassment when I was informed that my check to you (#[CHECK NUMBER]) was returned due to insufficient funds. That is why I immediately contacted my bank, who notified me that they had [BANK ERROR, ex. failed to process a deposit we made two weeks ago].
I have nonetheless enclosed a replacement check (#[CHECK NUMBER]) in the amount of $[AMOUNT]. My bank will be forwarding to you a letter of apology regarding their error.