Trigger and Function Question

I'm new to PostgreSQL and while it's been fairly straight forward
setting up, creating databases, tables, etc, I'm having trouble
understanding the correct creation of triggers and functions.

I have several tables with a timestamp field that I would like to use
a trigger to update whenever a row is updated.

I've created a function as follows

OS: Caldera OpenLinux eServer 2.3
PostgreSQL Version: 7.0.3

Create Function f_set_updated()
returns opaque
as 'Begin
new.updated = current_timestamp;
return new;
End;'
language 'plpgsql';

which return the Create message meaning it was accepted and created.

Next I created a trigger as follows

create trigger trig_t_user_updated
after update
on t_user
for each row
execute procedure f_set_updated();

This returned Create.

When I try to update table t_user:
update t_user set midint='X' where user_id = 'mmortar';
I get the following error:

010418.22:47:10.789 [29762] ERROR: fmgr_info: function 25479: cache
lookup failed
ERROR: fmgr_info: function 25479: cache lookup failed

What am I doing wrong??
What are some good reference books, sites to use as I'm learning?

Thank you

Jeff Umstead
jumstead(at)timlsoftware(dot)com