[otrs] Service field grayed out

Hi, I'm attempting to create a new ticket and assign it to a service. I already have a few services created, but when I create a new ticket, the service field isn't active and I can't assign the ticket to the service as it is shown here: http://doc.otrs.com/doc/manual/itsm/stable/en/html/ch06s02.html I'm running OTRS + ITSM Module at 5.0.19 Cheers, Pedro