INSERT INTO foo (col1,col2,...,coln) not working

INSERT INTO foo (col1,col2,...,coln) not working
INSERT INTO foo (col1,col2,...,coln) not working
INSERT INTO foo (col1,col2,...,coln) not working
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Why does this statement:

insert into Topos (IdLibro, Pagina, IdTopo, IdReferencia, PosX, PosY, Ancho, Alto) values
(CAST(Libro AS CHAR(6)), pag, CAST(Topo As CHAR(6)), CAST(Refe AS CHAR(6)), posX,
posY, Ancho, Alto);

gives me this error (the statement is on line 16 of a function, all aliases are ok):

WARNING: Error occurred while executing PL/pgSQL function instopo
WARNING: line 16 at SQL statement
ERROR: parser: parse error at or near "$1" at character 60

and on the other hand this statement;

insert into Topos values (CAST(Libro AS CHAR(6)), pag, CAST(Topo As CHAR(6)),
CAST(Refe AS CHAR(6)), posX, posY, Ancho, Alto);

works fine? The column names are ok i double checked that...

help! thanks

JuanF