Turning off Windows Virus and threat security eliminated the 'Debugger error' and also, of course, the Windows Security message. At least I can now get further into the process of tracking down this bug.
Both the exe and the dbg files exist in the expected folder with the expected time and size.
Thank you Martin for telling me about the ability to exclude just one folder from virus scanning. I feel a lot better about just one folder than the entire PC being "unprotected". When I excluded just the folder with the "offending" files - no error message - although my bug is of course still there.