Drag & Drop Monsters Not Working

The last day or so I've been assigning token pictures to my Monsters. When I drag the monsters onto the map, I get nothing... what is going on?

When you say token pictures, you mean the "mini" that you see on the map, correct? If this is so, after you edit the token, do you save the edited token as the default token for that sheet? This must be done as the last step in any token modification for the default to "stick". See  Linking Tokens to Journals  in the wiki. If I am misunderstanding the issue, please give some more detail. I'm sure we can work through it.