Google Adsense internal search code does not work with Drupal sites normally. The reason is $_GET[q] conflict between both services. $_GET[q] means "current page" for Drupal and "search query" for Google. We can fix it with two easy steps.
Step 1:
Create a custom page like "websearch" etc under Drupal and add Adsense Code for results page.
Step 2:
Add this code at the top of your Drupal's index.php:
Google's solution
You can try to use
var googleSearchQueryString = "z";
parameter for search results. And don't forget to change this input name in search form, ofcourse.
Enjoy.
Added to DrupalSightings.com