Pete,
You will recall our exchange of messages regarding this same issue.
And I am wondering suddenly upon reading this post whether or not I advised you of my findings a while ago. I thought I did but I suddenly got doubts. Regardless, here it is again: I fixed my problems by ensuring no other application ( in my case it was IVAP) looks for Weather information at the same time as FSX does. You were right from the beginning i.e., it is a SimConnect problem. I also advised Microsoft as advised but I got their generic response as others did.
Anyway, since I disabled Weather in my IVAP configurator (which is IVAO software - does the same as VATSIM), I do not get those nasty memory popups anymore. A thousand thanks once more for leading me to the right track
Jean-Guy