[otrs] Attachment not working : "Need ContentType !"

Hi again, I'm trying to send an email to OTRS with an attachment (a small ascii file named error.log created with notepad). The system receives the e-mail, creates a ticket with an attachment named 'filed-1', containing the message body, but no attachment for the error.log file. In the OTRS logs I get the error "Need ContentType !" at the same date as the ticket creation. I am using OTRS 1.2.1. Any help would be appreciated, Brice