Depending on how you upgraded your DNN site you may be missing a key in your web.config file that can cause the preview to load an empty box and cause search to not return results.

Make sure you have the following key in your web.config file to correct this behavior.

<system.web>

   <httpModules>

      <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />

   </httpModules>

</system.web>

Applies to Active Forums 3.7, DotNetNuke 4.5.0,4.5.1