Why would query return PGRES_NONFATAL_ERROR?

I'm using 7.3.2, invoke a small stored procedure via PQexec, and
PQresultStatus returns PGRES_NONFATAL_ERROR. I can find nothing in the docs
to help me understand what could cause this, and PQresultErrorMessage is
blank.

This is pretty rare; most of the time by far the stored procedure executes
and I get the correct result back. I have almost no clue about what's
different when the failure occurs. I did notice this last time that there
was a backend stuck in a state with a transaction open forever. Could that
be it? A write lock conflict?

I've gone into postgresql.conf and upped the logging info. Any clues as to
what I should be looking for?

The stored procedure in question returns a longint, and when getting any
kind of error indication I don't examine its results. Should I be going
ahead and using PQgetvalue after getting a non-fatal error???

I guess next I should look putting some debug code into the stored procedure
to log its progress...

--
Scott Ribe
scott_ribe(at)killerbytes(dot)com
http://www.killerbytes.com/
(303) 665-7007 voice