User Interface Messages
Message boxes—sometimes called error messages or pop-up messages—are secondary windows dedicated to delivering messages about a particular situation or condition. Messages can contain information about the result of a command or action (an informational message), about the potential outcome of an action or condition (a warning message), or about some unforeseen action that has occurred (an error message).
For guidelines on writing event-log messages, see Event Logs.
Messages should be concise, specific, and helpful. Particularly in the case of an error message, you should include the issue, the cause, and the user action to correct the problem.