GWIA moves mail to GWPROB : Unicode string translation

Hello
Some mails are being stopped by the GWIA agent and the log is like this :

23:38:17 5A0 MSG 1061242 Processing inbound message: LOG-GW/DATA:\GRPWISE\LOG-DOM\WPGATE\GWIA\receive\768D8C15.401
23:38:17 5A0 MSG 1061242 Sender: mts@arkom.co.il
23:38:17 5A0 MSG 1061242 Recipient: lior@ashdot.org.il
23:38:17 5A0 Fatal error processing message
23:38:17 5A0 MSG 1061242 Converting message to MIME: LOG-GW/DATA:\GRPWISE\LOG-DOM\WPGATE\GWIA\send\x1c8d869.852
23:38:17 5A0 MSG 1061242 Queuing message to daemon: LOG-GW/DATA:\GRPWISE\LOG-DOM\WPGATE\GWIA\send\s1c8d869.852
23:38:17 5A0 Truncation in Unicode string translation conversion (840A)
23:38:17 5A0 The message was moved to: LOG-GW/DATA:\GRPWISE\LOG-DOM\WPGATE\GWIA\gwprob\51c8d869.BAD

Can anyone help ?
Beeri