Windows File Sharing Orphaned File Locks

Grab Handle.exe (http://technet.microsoft.com/en-us/sysinternals/bb896655.aspx) and, on the server computer, run a "handle -a" redirecting the output to a text file. Search that for the affected filename. That should at least tell you what process on the server computer has an open handle to the file. I'd be interested to know what process has a handle to it. (I'm wondering about anti-virus software as a possibility...)

My condolences for having to deal with GlobalShop, BTW.

Edit:

McAfee VirusScan 8, eh? Have a look at this: https://kc.mcafee.com/corporate/index?page=content&id=KB52156

It refers to Microsoft Office files, but it sounds suspiciously like it could affect any type of file. See also:

http://forums.mcafeehelp.com/showthread.php?t=223545

http://www.tek-tips.com/viewthread.cfm?qid=1453943&page=1

https://web.archive.org/web/1/http://techrepublic%2ecom%2ecom/5208-6230-0.html?forumID=101&threadID=207897&messageID=2632853

Procmon might be your best solution here as it is able to log what processes are using what files. Even if the file isn't showing up in openfiles procmon will log who opened it. Antivirus software is the usual culprit in these cases.