Hi! OneTinSoldier66
hi!
I also had this problem before, and it troubled me for a long time, now i've finally got the problem solved! And i'm freaking excited now...anyways, here's the solution:
1.open the pmdg opetion center
2.click ''please select a product'' and select your aircraft
3.click ''livery downloader'' and download a livery(you can download one randomly)
4.don't close the pmdg oc, and go to the directory of your ptp file
5.right click on it and choose ''open with pmdg operation center"
6.there you go!