Forum OpenACS Development: Problem with mailing list in creating a new job

i'm not able to create and test a mail job, i created a mailing list and a mail class, i inserted all the value for a job, but at the end (http://mysite.com/.../mailing-list/madmin/jobs) the system tell me:

"Problem with your input
We had a problem with your input:

You must supply a value for class_id

Please back up using your browser, correct the above , and resubmit your entry.

Thank you.

How can i fix this error?