Even if the template somehow, managed to save without showing you an error message, the ads will not show. I have received series of complaints from some Bloggers, saying their ads fail to show on their blog, despite following the right instruction of adding Adsense in Blogger template. Well, if that ever happens to you, then you should know that you have made one mistake ---- You did not parse you code.
So, What is the way out?
When you copy the adsense code from you account, you will have to paste it in the form on the site to parse it or encode it. After pasting your code ,you will have to click the Parse button. The page will reload and you will see the parsed code. If you insert this parsed code into your Blogger template, you will not see any error and when you view your blog, your ads will be displayed.
You can bookmark the page so you can easily locate it whenever you need it.