This question crops up often:
when customizing my blog, I click on 'add a page element', then I click on 'adsense' and this is what comes up.....
Please correct the errors on this form.
Format: 300 x 250 Rectangle (drop down menu)
Blogger is not allowed to request ad code for your AdSense account. You must fix this by signing in again and allowing Blogger to manage your account.
My recommendation is, forget about adding AdSense products direct via Blogger except if you want to add AdSense ads between posts (click BACK button to get back to this page). Reasons: You have much limited options like being unable to add AdSense custom channels and Adsense text or button referral links, or even Google site search box.
Use this method: Adding Adsense products to Blogger blogs. No time to check what is inside there, but perhaps you can get more information from Blogger Beta: Adding advertisement and hit counters, etc (click BACK button to get back to this page). Feedback highly welcomed as some may need updating.