Unicode errors?

The following message have been reported in the logs during data insertion:
++++++++++++++++++++++++
DBD::Pg::st execute failed: ERROR:  Invalid UNICODE character sequence
found (0xc567)
DBD::Pg::st execute failed: ERROR:  Unicode >= 0x10000
DBD::Pg::st execute failed: ERROR:  pg_atoi: error in
"0112022200@host.name": can't parse "@host.name"
++++++++++++++++++++++++

Others unicode numbers and email addresses have been logged.
The were proplems with the data import before, I got :
    ++++++++++++++++++++++++
   Wide character in subroutine entry at
/usr/lib/perl5/5.8.0/i386-linux-thread-multi/Encode.pm
   ++++++++++++++++++++++++
So LANG was set to C, and the problem disappeard.
What could be the cause of the problem?

perl-5.8.0-88
perl-DBI-1.32-5
perl-DBD-Pg-1.21-2
postgresql-7.3.2-3
Redhat 9 (2.4.20-8smp)