Invalid byte sequence for character encoding 0x00 after upgrading from 8.3 to 8.4

Invalid byte sequence for character encoding 0x00 after upgrading from 8.3
to 8.4

I'm trying to upgrade a database from PostgreSql 8.3 to 8.4, I backed up
the data from 8.3 and restored from 8.4 without issues, but, when I try to
use the same program that is working perfectly connected to 8.3, it throws
the error:
Invalid byte sequence for character encoding <<WIN1252>>: 0x00
Does anyone know what can be happening?.
SOLVED: Pg 8.4 is more strict when dealing with characters, hence the
error. It was my program that was trying to insert \0 on a field. This
forced me to debug my program and solve the problem.