Cache.get 'reponses' return nil help! help!

Hi all,

I want to cache some objects (models) in memcache, it stores the data successfully using (Cache.put statement) but while retriving the stored data from memory using (Cache.get statement) it return nil value. It goes something like this..

if Cache.get 'responses'!=nil        @responses=Cache.get 'responses'      @responses_pages=Cache.get 'response_pages'      @advertiser=Cache.get 'advertiser'     else

      if @@security.checkSecurity(session[:userName],session[:securityToken],8)==0         @advertiser = Advertiser.find_by_user_id(session[:user_id])        @response_pages, @responses = paginate :responses, :per_page => session[:record] ,:conditions=>["advertiser_id=?",@advertiser.id] ,:order=>'id desc'      Cache.put 'responses', @responses      Cache.put 'response_pages', @responses_pages      Cache.put 'advertiser', @advertiser

Any suggestion will be appreciated! Thanks in advance