Effective Error Messages
http://infocentre.frontend.com/infocentre/articles/effectiveerrormessages.html

Gaine, Frank
Frontend Infocentre
2000

Abstract:

State-of-the-art usability engineering should eliminate user errors. But in the real world, those users (the majority) who do not read instructions and prefer to 'figure things out as they go' are inevitably going to come unstuck occasionally. In these situations, interface designers must ensure that the feedback provided is as helpful as possible in setting the user back on the right track. Unclear and unhelpful error messages tend to mean that errors will recur, or take longer to resolve. The resultant frustration can lead users to mistrust the interface or even abort the task in question. This result can be disastrous, if for example it happens during the course of an online reservation or purchasing process.