[otrs] Problem creating ticket

Hello. I am installing a new OTRS machine, and for one user, the ticket request via web works as expected, but for another one, when he tries to create a new ticket (with the same exact type, To, Service and SLA), it gives an error "Can't get ArticleID from INSERT". The ticket, however, is created, but no email is sent. Both users belong to the same group and have access to the same services. Can anyone point out a solution? Thank you, Nuno