When starting a published application in Parallels Client for Mac or Linux, following error message is displayed, accordingly:
Error 66: An internal error has occurred.
Parallels Client 15.5 for Mac uses RemoteFX graphic acceleration.
Parallels Client for Mac doesn't support Lossless image quality for a RemoteFX graphic acceleration.
Edit RemoteFX image quality GPO on Terminal Server(s):
Start gpedit.msc and go to :
Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Remote Session Environment
Change “Configure image quality for RemoteFX Adaptive Graphics” value to High.
Alternatively, you may disable RemoteFX graphic acceleration in Parallels Client > Connection Properties > Display