Problem Creating view Pervasive 8

I all.
I have this problem.
command...

create view vistamom (NumFattura, Data, importo, Causale, contropartita)

as
SELECT F.NumFattura, F.Data, F.Importo1 as importo, F.Causale1 as causale, '1' as contropartita
FROM RIWTE_Fatture as F
WHERE F.Importo1 is not null AND F.Importo1 <> 0 AND F.Categoria = 'Libera'


Error reported.
The table has index on NumFattura, Data
The table is empty
When the table is compiled no duplicate rows are in.
Please Help.
Thenka Alessandro Zambonin
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ODBC Error: SQLSTATE = S1000, Native error code = 0
Unable to create table vistamom.
The record has a key field containing a duplicate value(Btrieve Error 5)



create view vistamom (NumFattura, Data, importo, Causale, contropartita)

as
SELECT F.NumFattura, F.Data, F.Importo1 as importo, F.Causale1 as causale, '1' as contropartita
FROM RIWTE_Fatture as F
WHERE F.Importo1 is not null AND F.Importo1 <> 0 AND F.Categoria = 'Libera'
Some error(s) encountered while executing SQL statement(script).