When I started on the project this morning, I tried Erich's suggestion first. It worked, so I was off and running.
However, later, I ran into the same problem again! Although I was not trying to rename a project, the first clue was that when I tried to "Clean", I would get an error message. So, this time I tried Alice's suggestion, but I did it in Windows Explorer. This was fortuitous in that when I tried to do it, I got an error message that the file was in use by the debugger - even though I had exited KDS altogether.
I reset the machine and was able to delete the file and continue. However, it indicates a possible problem with how a debugging session is closed. If the 'elf' file is still marked as in use by the debugger, it's an impasse and nothing gets done.
As far as I know, the only way around this is to reboot the machine. That's a REAL pain!