When I select a section of a drawing and I copy it, then try to paste it into a different drawing that has the same need for this selection.  When I paste it, I lose some of the blocks that are in this selection.  I am not sure if it has something to do with duplicate blocks, but any help will be greatly appreciated!!

Are all the layers turned on in the new DWG?Are the items which are not being copied on a locked layer in the source DWG?

Yes? No? Maybe?

I actually figured it out the other day. It was due to the blocks not being properly defined in the drawing that I was pasting them to.
 
Thank you for the help.

Thanks for letting us know about the solution.