Undocumented Postgres error: "failed to fetch old tuple for AFTER trigger"

I'm running a very large series of commands - mainly DDL but some DML as well - in a large transaction.  I get the following error, which doesn't seem to be documented:

"ERROR: failed to fetch old tuple for AFTER trigger
: COMMIT"

There are no triggers that I'm aware of.  I've gotten this error when running the transaction on two different instances of the database.  I also did a VACUUM FULL, which didn't help.

Breaking down the commands into a series of about 7 smaller transactions works fine.  Each transaction runs totally fine by itself.  But, when I run them all in one giant transaction, I get errors.

I'm running Postgres 8.2.1 on Windows XP.  If anyone can help, I'd be very greatful.