plpgsql error: cache lookup from pg_proc failed

playpen=# create table aa(
playpen(# a int,
playpen(# b int,
playpen(# t timestamp
playpen(# );
CREATE
playpen=#
playpen=#
playpen=# CREATE FUNCTION touch () RETURNS OPAQUE AS '
playpen'# BEGIN
playpen'# new.t := current_timestamp;
playpen'# RETURN new;
playpen'# END;
playpen'# ' LANGUAGE 'plpgsql';
CREATE
playpen=#
playpen=#
playpen=# CREATE TRIGGER lastmod_1 AFTER update or insert ON aa FOR EACH
ROW EXECUTE PROCEDURE touch();
CREATE
playpen=# insert into aa (a, b) values (1,2);
ERROR: plpgsql: cache lookup from pg_proc failed

What does this error message mean?

--
Joseph Shraibman
jks(at)selectacast(dot)net
Increase signal to noise ratio. http://www.targabot.com