Thanks for that, Umberto. I'll try your suggestions
I was using PlanG while FSX was running but that is my usual procedure. Since restarting FSX after the last freeze, I have not run PlanG and the freezes are shorter. I also run REX Weather Engine with FSX.
So I'll try without either and with a default aircraft and report back to the forum...
Mark (or should I call myself 'Marco'?