sorknes

Found the problem!

There was an error in my searchform.php:

<form action="/" method="get">
    <fieldset>
        <input type="text" name="s" id="search" value="<?php the_search_query(); ?>" />
        <input type="image" alt="Search" src="<?php bloginfo( 'template_url' ); ?>/images/search.png" style="background-color: black;" />
    </fieldset>
</form>

Used this function instead:

function my_search_form( $form ) {
	$form = '<form role="search" method="get" id="searchform" action="' . home_url( '/' ) . '" >
    <div class="searchform">
    	<label class="screen-reader-text" for="s">' . __('') . '</label>
    	<input type="text" value="' . get_search_query() . '" name="s" id="s" placeholder="Start typing here..." />
    	<input type="submit" id="searchsubmit" value="'. esc_attr__('Search') .'" title="Search my site" />
    	<div class="clear"></div>
    </div>
    </form>';

    return $form;
}

add_filter( 'get_search_form', 'my_search_form' );

Problem solved!

Thanks for your suggestion esmi, but same error occurs. Any other suggestions?