You must generate Parsed code for your adsense codebecause you cannot put adsense code directly in the xml.So parse it using Adsense Parser tools.This tool help your visitors to parse their adsense code.I found this tips fromhere .
1.Login to your dashboard--> layout- ->Page Elements
2.Click on 'Add a Gadget'.
3.Select 'HTML/Javascript' and add the code given below and click save.
It will look like this.
Now you are done.