Table Function error: wrong number or types of arguments

I am developing an application in Oracle 10.2.0.3.0.

This is my first attempt at using Table functions.

The code below is giving me the error

        Errors for FUNCTION TABLEFUNCTION:

	LINE/COL ERROR
	--------
-----------------------------------------------------------------
	18/11    PL/SQL: Statement ignored
	18/21    PLS-00306: wrong number or types of arguments in call to
'TAB'
	18/21    PLS-00306: wrong number or types of arguments in call to

thanks

	drop table TABLE_A;
	drop table TABLE_B;
	drop function tablefunction;
	drop type tab;
	drop type ntt;

	create table TABLE_A
	(
	  COL_AA INTEGER not null,
	  COL_AB VARCHAR2(2000) not null,
	  COL_AC VARCHAR2(30),
	  COL_AD INTEGER not null,
	  COL_AE TIMESTAMP(6) not null
	)


	/


	create table TABLE_B
	(
	  COL_BA INTEGER not null,
	  COL_BB VARCHAR2(50),
	  COL_BC INTEGER not null,
	  COL_BD VARCHAR2(1000) not null
	)


	/


	CREATE OR REPLACE TYPE ntt AS OBJECT
	(
	       x          INTEGER,
	       y          VARCHAR2(2000)
	)


	/


	CREATE OR REPLACE TYPE tab AS TABLE OF ntt


	/


	CREATE OR REPLACE FUNCTION tablefunction
	RETURN tab PIPELINED
	IS
	  rt_a table_a%ROWTYPE;
	  my_ntt tab;

	  CURSOR my_cur IS
	  SELECT *
	  FROM   table_a;

	BEGIN

		OPEN my_cur;
		LOOP
		  FETCH my_cur INTO rt_a;
		  EXIT WHEN NOT my_cur%FOUND;

		  PIPE ROW (tab(rt_a.col_aa, rt_a.col_ab));


		END LOOP;
		CLOSE my_cur;

		RETURN;

	END tablefunction;


	/