Unable to Copy Elements from One Project to Another

[Anonymous]

I am attempting to copy and paste 3D elements from one project to another project open in the same instance of Revit. I have opened the floor plan views in both projects and the 3D view in the original project. After clicking and dragging the cursor to highlight all 3D elements, I went to the floor plan view to copy the items and pushed Ctrl + C, but rather than copying the items, two warnings came up (see attached). I've never seen this before, and haven't found any solutions on any forums. Any suggestions would be appreciated.

[EMCINERNEYNDQFH]

If you expand the warning it will tell you exactly what elements cannot be copied. I would still copy/paste anyway most of your elements will still copy over...

[kadmonkee]

if elements are pinned they will not copy.

if elements are in a linked model they will not copy either so be careful what you capture to copy

use the copy to clipboard tool from your host project 

move to the recipient project then use the Paste options

face hosted or other hosted elements will not paste unless a similar host is available in the new project