SQL & PL/SQL

I am using the comma_to_table listing have you any idea why I might be getting this :
BEGIN
*
ERROR at line 1:
ORA-00931: missing identifier
ORA-06512: at "SYS.DBMS_UTILITY", line 79
ORA-06512: at "SYS.DBMS_UTILITY", line 108
ORA-06512: at "QPI.SPCOMMATOFILETBLUSERSITES", line 7
ORA-06512: at line 2
when I try running the comma to table stored procedure while not passing in "s" it works ok, however when I try passing in "s" I get errors in my SQL*Plus worksheet application ?
This is what I use to run stored proc :
set serveroutput on;
BEGIN
spcommatofiletblusersites('1,2,3,44,5');
END;

This is the stored procedure :
PROCEDURE "SPCOMMATOFILETBLUSERSITES" (sa IN VarChar2)
IS
s varchar2(30) := sa;
a dbms_utility.uncl_array;
len integer;
begin
dbms_utility.comma_to_table(replace(s, ',', ','), len, a);
for i in 1..a.count loop
dbms_output.put_line( a(i) );
end loop;
end;

New info : The stored procedure runs when I put double quotes around each character in the string like below :
set serveroutput on;
BEGIN
spcommatofiletblusersites('"1","2","3","4","5"');
END;
Output :
"1"
"2"
"3"
"4"
"5"
PL/SQL procedure successfully completed.
But this is no use to me as I will be using a comma seperated file with
possibly 000's of elements so the file cannot be updated to incl " " around
each element.

Any Ideas ?