If you drag an image out of a project into another project and don't have the option key held down then Aperture will always do move.
One thing to look for if you're doing a move when you drag to the new project the project will highlight, if you are doing a copy the project will highlight AND you will see a green plus sign. You can observe this by dragging without the option key and while hovering over the new project press the option key, you'll see the green plus sign.
If you see other behavior you should start with Aperture 3: Troubleshooting Basics
Thank Frank and Kirby...
I missed that point in my OP ... thus the "randomness". I had sent the files to Facebook after import as all the photos fit the subject at that time. Then, afterwards, I wanted to move the files from the Project where they did not really belong to another project and that is when they would not move... so, the answer seems to be the problem is a result of sending them to FB.
I do know about the difference between the highlight and the highlight with the + sign. It is interesting in this case that the action generates highlight only, but does do a copy. That is likely again because of the FB thing.
So, I can copy the images, but I guess the originals are simply stuck in the wrong project.
Would removing them from FB make any difference?