For years, developers (and designers) have heard me rant about error messages.
Way to go AOL !
Those that know me, know that over the years I have been on a personal crusade to help developers figure out ways to improve error messages. I've worked a lot with technical writers, and with many developers over the years and have a pretty good idea how to get this done.
You need to think about errors in advance and develop a common error message strategy. Anticipate the types of errors that may display, and create both a visual and textual template for each. Informational messages, for example, should display and be worded differently than warnings, errors and critical errors. Make sure that the error messages don't blame the user, but provide useful advice on what caused the error and how to solve it. Your end-users will be much more happy and productive.
update: I just saw this error message in an online form and I HAD TO POST IT. OMG!!!