You might want to right-click on the Project Tree, and select Collapse All. Then, make sure there is at least some white space at the bottom below where all your process flows are listed. If not, you may need to expand the screen real estate dedicated to your project tree. Once you have available white space, right click, and hopefully Paste will appear as an option instead of being grayed out. This is how it's working for me anyway, and since I finally figured it out, I wanted to share.
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