Here is the problem. After copying or reinstalling OS X using 'archive and install,' did you suddenly discover that you can't drag and drop a file onto Photoshop's dock icon? This was quite frustrating and after some digging I found the solution and thought I would share a simplified version here in case this has happened to others.

If you are having this problem, you're most likely missing an important file called Adobe Unit Types, which resides in the top-level Library -> ScriptingAdditions folder (create the ScriptingAdditions folder if necessary). Then just drag Adobe Unit Types from the same location in your Previous System folder into the current Library -> ScriptingAdditions folder (quit all Adobe apps first), and you're done. Enjoy Photoshop once again.