"unicode" warnings

I am curently import data into rt 3 (3.0.7_01) and I have the followign
message repeated in the logs
for each binary Attachments:
[warning]: DBD::Pg::st execute failed: ERROR: invalid byte sequence for
encoding “UNICODE”: 0xe0 at
/usr/lib/perl5/site_perl/5.8.0/DBIx/SearchBuilder/Handle.pm line 410.
The attachment is subsequently not created.

What could be the cause of this problem, and how can I solve it?