missing esp32_ulp

[krismc]

Greetings snake charmers*. I've got a couple of esp32S2s that seem identical, both report

>>> import os; os.uname()
(sysname='esp32', nodename='esp32', release='1.23.0', version='v1.23.0 on 2024-06-02', machine='Generic ESP32S2 module with ESP32S2')

But when I try to run my program, one of them throws an error

Traceback (most recent call last):
  File "<stdin>", line 74, in <module>
ImportError: no module named 'esp32_ulp'

The offending line is

import esp32; ulp=esp32.ULP(); from esp32_ulp import src_to_binary

I can't figure why the module has gone AWOL on one of the boards & what I need to do to fix it. Any suggestions?
* Those of you that struggle less with python than I do, after 9 years it still bites me occasionally!