It could be because of set exclusive is ON. Or in the program there is a command that needs exclusive access to the file (like copy to, rename, etc..)

>Recently I have been getting deadlocks in my application.
>What causes a deadlock ?
>Can it be avoided ?
>How can it be resolved ?
>What causes the "File is in use by another user" to be generated ?
>I understand how a record can be in use by another user but why the file ???