>>>>>>We had such problems before in my former job place. Once the file got locked, only re-booting the computer in question released this lock.
>>>>>
>>>>>We had to reboot a few times, too. At other times, I just boot the users (if a file called "maintenance.tmp" exists, the application quits automatically), but this doesn't always work.
>>>>>
>>>>>And, sometimes the problem disappears by itself after a few minutes.
>>>>>
>>>>>The problem is, this is happening almost every day, recently.
>>>>
>>>>What kind of file it is? Dbf?
>>>
>>>Yes, DBF. - As Borislav pointed out, if it is opened exclusively, then only one user has it open. Strangely, I hadn't thought about this.
>>
>>I tried to tell you that in my first message, sorry if it was unclear. So, you resolved your problem?
>
>Well, it is one of those errors I can't provoke, rather, I have to wait if it happens again! Also, I am not at work now. I will have to grasp the "opportunity", next time the error appears - if it appears again - to fetch more information.

You could consider to deploy small 'application' that will permannently hold the file open in shared mode; so you would have to wait for easier identifiable event when some client workstation with faulty process bombs.