> Is that application installed on one computer or database resides somewhere on LAN?
Not necessary, it also happens local.

> Is it possible some other user to LOCK the table (or use it EXCLUSIVE)?
No. We have only one homemade zUse() function and all tables are opened passing by this function.
The table are opened SHARED without any other clause, except AGAIN maybe. And if that was EXCLUSIVE,
not supposed to be READONLY.. because already opened.

> When you get that error can you copy and after that delete some file in the folder where tables are?
The next time i will try that. I remember to have already check with LIST STATUS while program suspended (on error),
I can see the table is display READ-ONLY. Very strange !