The On Error action enables you to control what should happen if an error occurs on any action following the On Error action. You can add any number of On Error actions to an Automation.
Each On Error action can be set to:
If no On Error action is used on an Automation then by default ThinkAutomation will stop execution of the current message when an error occurs, send a notification email and pause the Message Source. This enables you to investigate the error before more messages are processed. You must then re-enable the Message Source to continue processing.