Originally posted here: usa.autodesk.com/getdoc/id=TS14206145

When you try to start XSI.exe or xsibatch, you get a pop-up dialog box that looks something like this:

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XSI
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Unable to access c:\Softimage\Softimage_2010_x64Data\Preferences\Default\OutputFormat\Cine_16.xsipref
Another process is currently using it.
Click Cancel to continue.
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Retry   Cancel   
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The actual file could be any file in the factory location or in a workgroup location. When you look in the specified folder, you find a .lock file for the file that could not be opened.

Typically, there are two situations when you may encounter this problem:

• When you run multiple instances of xsibatch on a single computer
• When multiple xsibatch jobs on multiple render nodes try to load a workgroup from a network server

The .lock files are created when a process (like xsi.exe) opens certain files (.xsitb, .xsicompound, .xsiprefs, and a few others) through the Windows API. Usually you’ll never see the .lock files. But if something happens to interrupt the file access (such as a network problem), you can get .lock files left around, which causes a sharing violation the next time a process tries to access the file.

You might want to try Process Monitor or Process Explorer to see what is going on. If you cannot delete the .lock file, try using Process Monitor to free the .lock file handle.

A possible workaround is to make the folder read-only, so xsi.exe and xsibatch cannot write a lock file. Then there can be no concurrent access to the lock file.

Here’s a few threads about lock files:
compound locks
lock files causing render problems