See, my bank sold my account (and the accounts of everyone else in my area) to another bank to get approval for their merger with a third bank. Anyway, that means I had to change to new checks with new account numbers. But I screwed up and sent last month's bill in on an "old" check. Which got to the credit card company on the 12th, but still hasn't cleared.
I feel so very stupid right now. Stupid and ashamed of myself for the mistake.