windows - find out which computer has opened a file on Servers network share

I have a Windows Server 2008 and it shares a folder. Many clients access that folder and the inherit files. One client opens one dll file
sporadically with mode rw, so after that no other client can load the dll.

Now I want to determine which client does it. All tools I found:

• openfile


• net


• sharewatch


• NetShareMonitor

doesn't show me the Network client which opens the file in rw mode.

I think it is the antivirus programm, but I need to know which client has the file opend.

Edit:

• The clients are windows machines


• All clients use the same user, so I can't determine the client with the username