When attempting to preview a report template, the following message will display if any predefined settings are 'invalid':

"An error has occurred. Please check the layout for invalid script commands or settings or field keys"
(we are addressing the issue with the application crashing)

You will need to review the report template settings (a suggestion is to undo your last step) and attempt another preview.
If the application crashes again, you will need to review the report template again.