Hi Bill,
So that rules out any problem with drivers or video RAM etc. on the virtual desktop.
From what you've said, your problem is almost certainly caused because PCoIP is blocked somewhere between the View Client and the View Desktop via the Security Server. This is assuming that you've configured the PCoIP External URL to use the external/public IP address that the client uses to connect to the Security Server and have configured the Connection Server to gateway PCoIP connections (i.e. you've done the 3 steps in the topic).
When it is set up correctly, you'll see on the Security Server TCP 4172 connection inbound from the client. You'll also see UDP 4172 both ways between the Client and the Security Server. You'll also see on the Security Server an outbound TCP 4172 connection to the virtual desktop and UDP 4172 both ways between the Security Server and virtual desktop. If you look at the wireshark trace on the Security Server and any of these flows are missing, this will allow you to pinpoint the culprit blocking this. If you've blocked any of these, then expect a black screen.
Set it up as in the video in the topic I referenced and it will work.
Let us know what it was.
Mark