Message Dialog
Design a message dialog when you want to communicate to the user about a situation that is unexpected or exceptional with regard to a task they are doing. Use message dialog boxes only when a message is important enough that the user must know immediately.
Message Dialog guidelines
From the user’s perspective, the following are qualities of a well-designed message dialog page:
Is used only with regard to unexpected or exceptional situations, not for ordinary or routine dialog.
Presents a clear message in the user’s language and that the user finds valuable.
Has an icon associated to the message signaling the type of message, either information, error, warning, or confirmation.
Includes details only as required to understand the context for the message.
Provides one or more dismiss buttons with captions that unambiguously describes the function of each button.