If you duplicate content, you will violate Webmaster Guidelines: http://www.google.com/support/webmasters/bin/answer.py?answer=35769#quality That is part of AdSense Terms of Service. But is hard to say as I never saw Google giving an explanation that banned someone due violating Webmaster Guidelines. But duplicate content is a bad idea as you will probably get banned by Google Organic results and your site will not get visitors.
assuming you arent referring to duplicate content that is from another site with a copyright on it, then no, they cant ban you.
They don't use to ban, but check the TOS and you will see that they clearly state that is not allowed to have a duplicate content on your site: