I found my problem: I knew that SET EXCLUSIVE is scoped to the current session. So I put SET EXCLUSIVE OFF in the form's Init() and in the BeforeOpenTable() of the data environment. But the database seem to be opened *before* the Init() and BeforeOpenTable() method. So the database was opened exclusively.

I added a SET EXCLUSIVE OFF at the statup of the application and now I can open more than one session at the same time on the same PC.

Thanx for your responses