To answer my own problem (Since no one at EPiServer does it) The prolem is that when you create a new folder, there are no files there and you will not be able to drag and drop files. After I uploaded a file the "standard" way, I can drag and drop fiels AS LONG as I drop it over the line that shows a file. If I try to drag and drop files below this line (into the empty space), it will not be possible. I hope this "bug" get fixed in a later version.

do you know how delete a document in the filemanagerbrowser,i can't delete it,right-click function can't use.do you know why is this?

I just mark the file by clicking it and then click the red X at the top of the file manger menu panel.