This block is responsible for exiting the app with an error message.
When would this be useful? For instance, you might have a 'Decision' block checking if a new email from a customer has arrived, and if not, you may want to exit the app, displaying an error message 'The customer email has not arrived yet, please re-run this app at a later stage'. In other words, whenever you know that something can happen, and you want to stop execution at that stage, but you don't want it to be considered as 'successful' exit with 'Exit' block, then you can use this option.
How to use it? Just drag-and-drop the following into your diagram: 
Then select the block and enter your exit message in the configuration area:
Once your business app hits this block, it will exit, showing the error message you have provided.
What will happen after this block is executed? Your business app will be stopped and it will be recorded that it has exited with an error.
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