e-Newsletter theme customizer problem

When I try to create or edit a newsletter there is a javascript error on the customizer screen:

Uncaught TypeError: $(...).tabs is not a function
(anonymous function) @ customize.php?wp_customize=on&theme=iletter&newsletter_id=1&return=admin.php%3Fpage%3Dnewsletters:73

I can't view or edit the newsletter.

Mathieu Cabot
mathieucabot@gmail.com