There are two possible reasons. First, the website being searched might not be available. You can check that by going to the site directly. Each of choices at the left starting with Ancestry.com will take you to a page that includes a link for manually searching. Click on the manual search link to see if the site is up.
If you find the site is up, the second reason the search does not work is that the site may have changed how searches are conducted. We will change the Active Searches page when this occurs, but your browser may have cached an earlier version of the Active Searches page. To refresh your cache, go to the Active Searches page and then place your mouse in the frame in the lower part of the screen that contains the SEARCH buttons. Then refresh or reload that frame.