So, at long last I've actually got an optimisation study working, and rather well.
Having so far been optimising for displacement with a mass limit, I'm now trying to introduce some stress limits too. Unfortunately I'm getting the error above.
It's a simple static analysis that's linked to the optimisation, on a single part. There's only one static analysis defined, and one optimisation study. The measures give results when running the static analysis on its own.
What on earth is this about?