Endnote X7 Error "This file is in use. Enter a new name or close the file that's open in another program."

[yyhuang]

The exact problem just happened to me in EndNote X9 while I was editing the output style. I could not open my main library anymore. 

The solution to me was open or create any other library, then edit the same output style again, close the editing window then open the library that was “in use”. 

Hope this helps anyone who encounter to this problem.