idlelib/run.py imports math through about 3 intermediaries.  Hence it failed, and pyshell displayed the message in the .png.  Both modules can raise failure messages.  In #25514, the run.py message was revised to point to a new section of the doc: "Startup failure".  The second paragraph is

"A common cause of failure is a user-written file with the same name as a standard library module, such as random.py and tkinter.py. When such a file is located in the same directory as a file that is about to be run, IDLE cannot import the stdlib file.  The current fix is to rename the user file."

This is what Joseph should have seen.  I added a note to the issue to also fix the pyshell message to point to this section.

A better but harder fix would be to temporarily remove the user directory from sys.path so that user files cannot stop run's startup.