To kick it off, I got the following error this morning when I mis-typed my account number while trying to pay my electric bill online:
Account number does not match ^[0-9]{1,7}-[0-9]{1,7}$
For those who don't know, that's a regular expression, a commonly used notation for specifying text patterns in certain programming languages and text processing tools. I'm guessing the developer was either lazy, or forgot to replace the default message supplied by the web framework with a more human-friendly message.