problem with simlpe captcha

Hi simple captcha works fine on my app. recently I changed my hosting
provider and moved the app to new server. Here its not working and
throwing error

ActionView::TemplateError (undefined method `find_by_key' for
SimpleCaptchaData():Class) on line #246 of home/register.rhtml:
243: </td>
244: <td align=left>
245: <br/>
246: <%=show_simple_captcha
(:object=>"user", :label => "Robot Authentication (Case Insensitive)")
248: </td>
249: <td align=left>

Not sure why? Can anyone help with it please..........