Thanks,
That’s the one. I had a Σ in the comment field where I was doing linear regression.
it upset a PC running the latest version of MCUXpresso, but my laptop which was running an older version on Linux was quite happy.
There also seems to be a bug in this forum software. It lets me type the reply, then asks me to log in, then tells me that an unexpected error occurred and loses what I typed, so that I have to type it again.