One of my favorite websites, the Daily WTF, posted a laundry list of spot-on examples for how not to write an error message a few days back:
Press ‘Y’ if you promise not to do it again.
No! - Bad User!!! … Do not do this again!
Of course, I can sympathize with the developers who wrote these error messages. I understand the reasons why this seems like the better option, but still. Ultimately, you’re probably better off just biting the bullet and making your UI Text people write the error messages.