What is inside these images?
Are the linked to InDesign or are they embedded?
Are they grouped?
Can you show us a screenshot of the target problem with the selected object(s) and the layer panel open on that layer?
This happened when I selected 4 text boxes and an image in InDesign CS5 and
dragged it into a new Document in Indesign CS6.
It turned into an image and it did not appear in the links folder. It was
not possible to edit it. It printed ok.
I have a vague recollection that that is normal when switching between versions. Try it opening the first file in CS6, but don't save it after you copy.
Mentioning that little fact about version differences would have been appropriate in the original post...
Dragging within a version is fine, dragging (or copy/paste) from CSx to CSy is not.