Problems with pgsql 7.1.2 and ExecEvalExpr

[I was trying to send this earlier, but I think some settings on my client
munged the message...]

Greetings, it has been a while since I have been on any of these lists. I've
spent the last year or so working in a place that uses MySQL for just about
everything. This means that the last version of PostgreSQL I've seriously used
was in the 6.5 series (6.5.3 I think, but it's been a while).

I am working on a project where I want the features from PostgreSQL and pulled
7.1.2 from the ftp site, built and installed it. All went fine, no troubles.
[Found I was a bit rusty using some of the PostgreSQL since I got used to some
MySQL specific things, but that's another issue.]

I got the data loaded that I need to work with, and am having a problem
with one
specific query. It keeps dumping out with ExecEvalExpr: unknown expressiong
type
704. I've searched google and the only reference I've found for this in
PostgreSQL has been on the hackers list for version 6.5.

What is the typical cause of this rather cryptic message? In my case, I
have two tables (both with less than 100k rows), where I'm selecting values
from the database (no calculations, but am using AS to define column
headers), and that are matching based on two columns being equal and the
age() of a timestamp from each table being between '-00:00:04' and '00:00:04'.

Components of the query work fine on their own, but the entire query causes
the ExecEvalExpr error referenced.

I have one other question.

I have an ID column which is a bigint, and I have another ID column which was
created using SERIAL, so it is an integer.

Is it possible to use SERIAL to get a int8 datatype instead int (int4)?

Finally, is it possible to get unsigned integer data types in a table?

Thanks,
Greg

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