I cannot drag any file in Assets. What is the problem?
I cannot drag any type of file (jpg , png , fbx,obj,etc) from explorer. I have windows 8.1 . I have to import asset. But I cannot import a folder or many files at one time. I have to do it again and again.
What is the problem???
The problem is not simple!
I run it as admin. But problem is not solved.
Never had any issues like that. Usually you can drag any file type into your project panel. If it doesn’t work for you (for what reason ever), you can always open your assets folder in the explorer and copy the assets you need into your assets folder. If you switch back to Unity it will import everything you added to the assets folder.
If it really doesn’t work and you are sure that you don’t try to drag files from an archive, it’s something wrong with your PC / windows installation / Unity installation / anitvirus software
ps: Are you sure that Unity has write access to the assets folder? Maybe you set some strange folder permissions.
*** edit ***
Since i have windows 8.1 by now i come across such an “issue” as well. It’s a “security thing” of Windows. If two applications run on different privilege levels they aren’t allowed to communitate. If you run Unity with Admin privileges then it can’t take information from applications that run under user privileges. The Explorer (this includes every folder window as well as the desktop) runs with user privileges.
So the solution is to not run Unity with admin privileges ^^. I still never had any problems with Unity, but with other programs that i run with admin privileges for other reasons. It was quite annoying that you can’t use the drag&drop support but the open file dialog did work.
On Windows 8.1, I found that the problem was solved by moving the unity project files out of my documents ‘library’ and to “C:\Users\Username\Unity projects”. I noticed the address was something weird prior to moving it, so decided to try it and it worked!
No other suggested fixes did anything (see here), so I highly recommend Windows 8.1/Unity 5 users try this before reinstalling anything 
Note that in that link some people had success with starting Explorer with administrator privileges, didn’t work for me but worth a try (instructions in link).
Had this same issue with Windows 7 Pro, and Unity 5.1, but closing and reopening Unity also fixed it.
There’s another thread like this, and it looks like a lot of people are having this problem with Unity 5 in Windows 8. However, I had this problem and fixed it by closing the program and reopening it.
have the same problems. fixed after a clean deinstall - registry clean - install as admin
I have the same problem on Macbook, Mac Sierra OS
For me it was because I was trying to drag zipped files into it. Fixed by unzipping them first.
You can always use Import Assets if dragging is not working.