Photosho CS Problem - Can't drag a layer set from one document to another one

Question

I have two documents open
On the source document, i want to drag a layer set from this document to a new one, but its not letting me
What would cause this.
My structure for the source document is
>Set 1 Layer Set
     >layer
     > Adjustment Layer
     >background
Background
Structure of the target document
>Named Layer Set
     > Where I want to insert the Layer Set from source document
     >layer
     > Adjustment Layer
     >background
Background

Answer 1

No error message is given. I just can't drag it into the spot I want to drag the layer set to (its not an individual layer, its a layer set)
Basically, this is all I can do (have to do a correction on how the layers and layer sets work, missing one level from the original post):
I've attached images as well to illustrate
On my target document, I want to have the layer set go where the red text is:
>Content Layer Set
     >Named Layer Set
          > Where I want to insert the Layer Set from source document (Set 1)
          >layer
          > Adjustment Layer
          >background
Background
right now, I can only drag the layer set to this position:
>Content Layer Set
      > This is where the Set 1 from the source document can go, I can't drag it into the layer set below
     >Named Layer Set
          >layer
          > Adjustment Layer
          >background
Background
First Image I attached shows the Set 1 Layer Set, above the layer set I want to drag it into
Second Image I attached shows what happens when I try to drag the layer set into the named layer set; it comes up with the "no symbol"
No Error message is given