Можно ли программно узнать, какой процесс блокирует файл в сети?

http://technet.microsoft.com/en-us/sysinternals/bb897552.aspx

PsFile

The "net file" command shows you a list of the files that other computers have opened on the system upon which you execute the command, however it truncates long path names and doesn't let you see that information for remote systems. PsFile is a command-line utility that shows a list of files on a system that are opened remotely, and it also allows you to close opened files either by name or by a file identifier.

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How it Works

PsFile uses the NET API, which is documented in the Platform SDK.