Thanks for your suggestion, I have already fixed my problem with the panel .dll error
I installed three aircraft recently that the first two installed newer versions of visual studio. The error above only when shutting down FSX and FSX ran normally with no ill effects. All other programs/games unaffected. Removed the recently installed microsoft visual C++, FSX error gone.
Installed the third plane which also installed visual studios newer version the error message reapeared on shutdown again removed the latest installed microsoft visual studio C++ and no more errors.
I could replicate the error by re-installing microsoft visual studios C++ 2015/2017 seperately or the combined 2019 which combines all three 2015-2019.
The error message could be a generic error message.
Thanks again for your suggestion.