We are working on a fix, but in the meantime you can view your earnings by logging in to your AdSense account directly at http://www.google.com/adsense
Update, 2/17: This is fixed. Thanks for your patience.
The latest on what's still a problem, what's getting fixed, and what's been taken care of, direct from the Blogger team.
Adding or editing an AdSense page element from your Layouts section may return the error message "An internal error occurred. Please try again." As a workaround to this issue, copy your AdSense code from your AdSense account and insert it into an HTML/JavaScript page element in the layouts section of your blog.