Yelling doesn't help.
To preserve formatting in a posted query, surround it with BBCode [ code ] and [ /code ] tags (without the spaces). Look up BBCode for more information.
Formatting your query for readability ...
UPDATE table1.trafico
SET table1.trafico.RDocumentos=
(SELECT RD.Folio
FROM table2.vt_rdocumentos RD
JOIN table2.vt_rdocumentosdeta RDD ON RD.ID=RDD.RDocumentos
JOIN table2.vt_pedimentos P ON RDD.PedimentoID=P.ID
JOIN table2.vt_clientes C ON C.ID=P.Cliente
LEFT JOIN table1.trafico T ON T.RDocumentos=RD.Folio
WHERE RD.Placas='M3'
AND C.Numero='GM064'
AND RD.FechaEmision=CURRENT_DATE
AND NOT EXISTS (
SELECT table1.trafico.RDocumentos
FROM table1.trafico
WHERE table1.trafico.RDocumentos=RD.Folio
)
GROUP BY RD.Folio
),
table1.trafico.PapelesDespacho=1 ,
table1.trafico.HorapapelDesp=CONCAT(CURRENT_DATE,' ',CURRENT_TIME)
WHERE table1.trafico.ID='76'
AND DATE(table1.trafico.HorafacturaRec)=CURRENT_DATE
AND table1.trafico.PapelesDespacho=0
AND table1.trafico.Despachado=0
AND table1.trafico.Rojo=0
AND table1.trafico.Rojo2=0
AND table1.trafico.Libre=0 ;
The error message means exactly what it says: you can't specify a target table for update in a FROM clause. As the MySQL documentation page on Update says.
The simplest solution to your problem may be to turn that update statement into a SELECT, and when you're sure its results are correct, save the result to a temp table, then update from that temp table.