The event handler receives an argument of type ShowErrorEventArgs containing data related to this event. The following ShowErrorEventArgs properties provide information specific to this event.

The ShowError event is sent to the active WorkbookView just before an error message is to be displayed to the user, and provides the event handler with the ability to modify the error message text and caption or handle the event.

The ShowError event is always invoked on the thread which created the workbook view control, and a lock is always acquired on the workbook set associated with the workbook view control before ShowError is invoked.

Reference