DB error (Viewing Sent Messages)

When I enter the Sent Messages folder, the /logs/errors logs the
following:

[10-Mar-2006 10:26:25 -0500] DB Error: DB Error: constraint violation
Query: INSERT INTO messages (user_id, del, cache_key, created, idx,
uid, subject, from, to, cc, date, size, headers) VALUES ('2', 0,
'Sent Messages.msg', now(), '535', '535', 'Fwd: Reminder photo update
Wells & Harrisburg for Real Estate Book dead line', 'Marco Prechel
mprechel@stormreadybuilders.com', 'xxx
xxx@stormreadybuilders.com', '', FROM_UNIXTIME(2517457380), 45046,
'O:14:"iilbasicheader":25:{s:2:"id";s:3:"535";s:3:"uid";s:3: "535";s:7:"subject";s:76:"Fwd: Reminder photo update in /home/ swfl/public_html/webmail/program/include/rcube_db.inc on line 455

any idea?

--mp