I use a Plugin: “add widgets to page”.
Use the shortcode: [addw2p name=”WidgetName”]
This will add a new widget that is accessible from the Appearance->Widgets.
You can add “Text/HTML” into the new Widget created.
You can paste your Adsense code in here and the Ad will appear where ever you use : [addw2p name=”WidgetName”] in your page or post.
There seems to be a bug, and to overcome it, I use a random text first and then add Adsense Code.
Eg:
The Text inside the Widget->Text goes like this:
“
<script>
…Adsense Script…
…Adsense Script…
…Adsense Script…
</script>
If you want to add Adsense code into your SideBar, you can simply add the “text/html” into the SideBar and do the above mentioned to add your Adsense Code.