tuple concurrently updated

My application receives the folllowing error sometimes.

Any idea how to fix ?

Andrus.

7/XX000:Error while executing the query;ERROR:  tuple concurrently updated

CONTEXT:  SQL statement "DROP TABLE templsabi"PL/pgSQL function "drop_table"
line 2 at execute statement

SELECT drop_table('templsabi');CREATE TABLE templsabi AS
    select
      toode,
      osak as sihtyksus,
      partii,
      laosumma,

      1 as lj, 0 as st, 0 as vm,
      0 as kaubasumma,
      kogus,
      0 as kogpak,
      CAST('' AS CHAR(10)) as yksus,
      CAST('' AS CHAR(1)) as doktyyp
    from HETKESEI
    where true
 AND osak LIKE 'TARTU%' ESCAPE '!'

 AND toode='DIS123103'
;SELECT * FROM templsabi

drop_table is defined as

CREATE OR REPLACE FUNCTION drop_table(TEXT)
  RETURNS VOID STRICT LANGUAGE plpgsql AS $$
 BEGIN
    EXECUTE 'DROP TABLE ' || $1;
    EXCEPTION WHEN UNDEFINED_TABLE THEN
 RETURN;
 END;
 $$;