priv problem with stored procedure

I've created a stored procedure to allow users to change their oracle password from our Powerbuilder app. However, when I try to run it, I get an insufficient privileges error. I've granted execute access on the stored procedure and even running it as myself with dba priv's I get this error. The stored procedure is shown below anyone have any idea's:

Create Or Replace Procedure sp_change_password (i_client_id in varchar2, i_new_pass in varchar2) AS

v_cursor  Integer;
v_ret     INTEGER;
v_cmd	varchar2(50);
BEGIN
      v_cmd := 'ALTER USER ' || i_client_id || ' IDENTIFIED BY ' ||
i_new_pass;
	v_cursor := dbms_sql.open_cursor;
	dbms_sql.parse(v_cursor,v_cmd,dbms_sql.NATIVE);
	v_ret := dbms_sql.execute(v_cursor);
	dbms_sql.close_cursor(v_cursor);

-- 
Ellen_Russell_at_dg.com