Hi,

>In my base class I set DATASESSION property to PRIVATE DATASESSION. The forms based on that class have that property seted well but doesn´t work. If I manualy go into that form and "force" DATASESSION property (making it bold) it work's ok.

Do the other parts in your base class work OK? VFP might have use a different version of the class library of the parent class than you think, maybe an older version sitting around.