There are 10 threads at Google Groups about a bug that appears to be impacting many Google AdSense publishers. In short, when you go through the process of creating a new ad unit, you are taken backwards instead of to the ad code page.
When publishers click the "submit and get code" button, instead of being sent to the code page, where they can obtain the code for their site, they are sent back to the "manage ads" page.
Again, like I said above, there are now 10 threads that I know about at Google Groups on this topic. They are now all consolidated and references in this single Google Groups thread. In that thread, AdSensePro Stephanie said, "Thanks for compiling the threads on this issue! I'll take this back to the relevant teams to see if there are any known issues."
Forum discussion at Google Groups.