Problem with self-made plpgsql-function / casting

Hello,
I'm a newbie to postgres and trying to produce my first functions.
Everything works fine as long as it takes numeric parameters, but when I'm
trying to use varchar or text-parameters, it fails and throws the following
exception:
ERROR: function public.fc_editlanguage(integer, "unknown", "unknown",
integer) does not exist
HINT: No function matches the given name and argument types. You may need to
add explicit type casts.
So I thought I would have to use the pgfunction cast(parameter as type)
before working with the parameter within the function. Still, the same
exception is thrown and I haven't got a clue how to solve this problem. Hope
someone can help me out, here is my written function:

CREATE OR REPLACE FUNCTION "public"."fc_editlanguage" (id bigint, name
varchar, kuerzel varchar, active smallint) RETURNS smallint AS
$body$
DECLARE id bigint;
DECLARE varlanguage varchar(60);
DECLARE browsershortcut varchar(10);
DECLARE insertdate date;
DECLARE active smallint;

DECLARE varreturn smallint;

Begin
varreturn := 0;
id := $1;
varlanguage := cast($2 as varchar(60));
bowsershortcut := cast($3 as varchar(10));
active := $4;
if(id=0) then
insertdate := now();
INSERT INTO tbl_language (la_language, la_browsershortcut, la_insertdate,
la_active)
VALUES
(varlanguage, browsershortcut, insertdate, active);
else
UPDATE tbl_language SET la_language=varlanguage,
la_browsershortcut=browsershortcut, la_active=active
WHERE la_id = id;
end if;
return varreturn;
end;
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;

Greetings from Germany,
Moritz
PS: I'm using postgres 8.0 on a xp system