Weird Problem With PostgreSQL 7.3.1 and VB.Net Datagrid

Hi All,

I have a very weird problem which is occurring with a VB.Net app and
PostgreSQL 7.3.1. There is a form that has a standard .Net datagrid on it
that contains some data from a table in PostgreSQL.

Now, the datagrid has functionality to allow the developer to
programmatically determine what changes (if any) that have been made to the
grid by the user -- i.e. determine if any new rows has been added, any rows
modified or deleted.

These changes are then written back into the database by simply calling an
update function on a DataAdapter object.

Now here's the problem.....the application is working fine for a couple of
months with all inserts, updates and deletes carried out on the database
table without any problems. Now updates do not work with the dataAdapter
update where a 'DBConcurrencyException' is thrown -- i.e. the dataAdapter
object will check that the underlying row(s) to be updated (in the database)
have not been changed since the dataGrid was populated with the data. This
you can imagine, can be an issue if there are a number of users working on
the same data / form, however, I am getting this problem with only *ONE*
user. This problem seems to be isolated to a particular table as I have had
no problems with any of the other datagrids in the application that perform
insert / update / delete operations.

The bizarre thing is that if I backup the database, drop it, and recreate it
from the backup, then the application works fine again.....what is up with
that!?!?

This lead me to think it may have been a maintenance thing, so I tried to
VACUUM-ANALYZE the table in question, but that has had no effect.

Does anyone have any thoughts, suggestions?
TIA
-simon