In reply to Chris Hemedinger.

I had the same problem. I could copy and paste the process flow within the same project, but creating a new project or opening another one closed the open project and paste is no longer possible.

The trick turned out to be that I had to open a new instance of SAS Enterprise Guide. With both instances open, I am able to copy the process flow from the source project and paste it into the destination project. Until I tried it, I didn't think there was much chance this would work.