could not open relation: Invalid argument

Version: PostgreSQL 8.2.5 on i686-pc-mingw32

I recently started getting this error message randomly, "could not open
relation 42904/42906/42985: Invalid argument". I also got it for a couple
of other files. All three files are related to tables that have just a
single row each.

I googled the error message and found that this looks like a problem on
Windows (which I'm running until we get access to our Linux server) and
probably related to anti-virus scanning. Having run Oracle on Windows
before, I have experienced the problem with an anti-virus scanner locking a
file and causing the database to error. I thought I understood and fixed
the problem.

Today, I used pgAdmin to Vacuum Analyze the entire database. It flew
through this task as my database is fairly small. However, when it got to
the three tables that exhibited this error message, it hung. It took maybe
2-3 seconds to vacuum analyze each one of these tables.

Now I don't get it. Was there something corrupt in the file and it wasn't
related to the anti-virus scanner?

Jon