Hi Aleksey,
just to let you know...
the problem that I mentioned I solved in this way:

Instead of this code in BeforeUpdate event:

IF valorunitario = 0
MESSAGEBOX( "Valor não pode ser zero")
RETURN .F.
ENDIF

I am using this code:

IF valorunitario = 0
cUpdateInsertCmd = "RAISERROR('Valor nao pode ser zero',16,1)"
ENDIF

So, I replace the command that VFP will send to SQL, raising the error there. It work if you use ODBC.

Thanks.
Ricardo.