PL/pgSQL Trigger Problems

I'm having problems getting a simple PL/pgSQL trigger to work. I suspect
that something may not be set up correctly, but I have no idea what.
Specifically, I'm trying to get the example working in the 'PL/pgSQL Trigger
Procedure' section of the documentation (located at:
http://www.postgresql.org/docs/postgres/x4418.htm )

Earlier, it was telling me that there was a Parse Error when I tried to
insert a value. Currently the error message I get is: "fmgr_info: function
4605120: cache lookup failed"

And for what it's worth, I did install plpgsql for my database as detailed
in the example in the documentation (located at:
http://www.postgresql.org/docs/postgres/xplang.htm#AEN22060 ). Specifically
I executed both the CREATE FUNCTION and CREATE TRUSTED PROCEDURAL LANGUAGE
statements.

Any help would be most appreciated.

Gregory Wood