I used the Multiple Category Selection Widget in Big Feature:
http://wordpress.org/extend/plugins/multiple-category-selection-widget/
This plugin gives you the ability to provide your users with a widget full of dropdowns based upon parent categories and their sub-categories. Multiple subcategories spanning multiple parent categories (though multiple categories inside a single parent cannot be chosen) are chosen and intelligently filter your posts. Users should now be able to search for your post under all those categories!
However, if I search with this widget and there are no results found, the whole sidebar moves to the leftside of the page.
If i change the template to the WordPress Default 1.6 there is no problem.
I tried to change the archive.php but that didn't work out.
Please help me out.
Thank you.