My son was playing the game and after an issue that prompted him to sign back in, the character he was playing on was no longer present in the hero select.  Other characters were still there.  

We dug into the windows folders and figured out that the DAT file for his missing character is still in the Characters subfolder.  But it will not connect to the game.  

We tried copying that particular DAT file into a Characters subfolder on another computer but it didn't appear in that game either, although other copied DAT files did.  

How do we reconnect that DAT file to the game?