You must generate Parsed code for your adsense code because 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 from here .

Parsed code will look like this :

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.