Twenty Eleven: Search Form (searchform.php)

http://wordpress.org/extend/themes/twentyeleven

Download the theme, extract the theme’s folder and upload it to wp-content/themes. This will wipe out any changes you have made to the theme but then you shouldn’t be editing the Twenty Eleven theme. It is the default WordPress 3.2 theme and having access to an unedited version of the theme is vital when dealing with a range of site issues. Create a child theme for your changes. Once your child theme is active, we should be able to help with any customisations.