There is something wrong with Google's script that generates your ad code for adsense for search. If you an adsense user you must be facing this issue these days. If you are in this bot too you have few options here.
First one is to add a Search Widget to your blog by clicking on "Add Widget" in your blogger account. This will provide your users with a search interface. However, this can not be linked with your adsense account. In short you can no longer make money from your search based ads.
The second option is to use custom search engine which is available for free
