Guy.. this post did not work for me but, I did find a fix..
You need to go into your simulator Lockheed Martin
Double click on Prepar3D v3 scroll down until your find
Prepar3D.exe.comfig open with note pad and it needs to read this:
<supportedRuntime version="v4.7" sku=".NETFramework,Version=v4.7"/>
one this part is done it save. and put check mark back in the NET.Frame: see step 4 in this thread.. I'm back in business
Works for me.. :)