Can't save flight plan in FMS ?

[Grol]

I'm working through the tutorial flight again to test a few things and decided to save the flight plan to save entering it every time. The plan is complete in the FMC including the SID and STAR and approach and no discons. When I go to the Init/Ref Index page I see Save FPL on RSK6 but when I press the button nothing happens.

I'm watching the blahblah\etc\WASM\MSFS2024\justflight-aircraft-rj\work\JustFlight\FlightPlans folder which remains stubbornly empty, and there are no plans listed in the stored flight plans (RSK2).

Anything obvious I'm missing ?

Thanks

(edit - before anyone suggests it as a workaround, I have created the route with the required fuel / pax loads / altitude etc in simbrief, and it imports fine from there - without entering the flightplan I can be ready to start engines now before the IRS have even aligned lol)