have exactly the same problem by the end of 2019. I tried all possibilities (firewall out, run OC as admin, having newest OC etc.). Support from PMDG was also quite good in the beginning, but after the 3rd or 4th mail changes, when the possibilities to solve the problem became less and less, my ticket was deleted without further notice. On my request for an alternative download link, and my statement that such problem solutions are not the task of the buyer, this was not answered either, and deleted again. Quite honestly, this is completely unacceptable behavior. With PMDG I am ready for all times!