I have been receiving this error message since April 5:
Can't Generate Promo Code
We're having trouble generating the codes. Please contact App Store Developer Support for assistance.
I have plenty of promo codes remaining.
Also, when I click through to the contact page, I get a useless series of menus that let me specify my problem and no place to actually send a message. It just has two buttons ("Start over" and "Done").
UPDATE: After six (6) days of downtime, this appears to be fixed.