I expected to get an error message if a template is running and I click on the “cycle” circular icon in the Template Results window’s title bar. But the message text is perhaps a little inaccurate: Could not execute template because a program is already running.
Of course, 010 Editor doesn’t really run programs. Perhaps the term was used generically to mean “template or script”.
This is a very minor point and probably an easy fix, but I think fixing it could wait until you’re ready to address any other issues with the text of error messages, or with error handling in general.