From Xojo Documentation
Class (inherits from RuntimeException)
An EndException is raised when you call Quit. It causes the application to quit gracefully. Usually you do not see the EndException unless you use a "catch-all" exception statement.
|NOTE: Whenever you inadvertently catch an EndException, you MUST re-raise it. Failing to do so will confuse the runtime environment and lead to unpredictable problems. See Exception statement for more information about its proper use.|