[Server Model] Cannot get personal social feed

Hi All,

I'm using the following code to get personal social feed,

SPSecurity.RunWithElevatedPrivileges(delegate()
{
   using (SPSite site = new SPSite(serverURL))
   {                     
      SPServiceContext serviceContext = SPServiceContext.GetContext(site);
      SPSocialFeedOptions feedOptions = new SPSocialFeedOptions();
      feedOptions.MaxThreadCount = 10;
      SPSocialFeed everyoneFeed = feedManager.GetFeed(SPSocialFeedType.Personal, feedOptions);
   }
}

but exceptions are thrown:

SPSocialFeedManager.GetFeed: Exception: Microsoft.Office.Server.Microfeed.MicrofeedException: ServerErrorFetchingActivityFeed : ( Value cannot be null.  Parameter name: serviceContext ) : Correlation ID:00000000-0000-0000-0000-000000000000 : Date and Time : 1/30/2013 7:54:39 PM    
 at Microsoft.Office.Server.Microfeed.SPMicrofeedThreadCollection.AddActivityEventsToThreadCollection(SPMicrofeedRetrievalOptions retOptions)    
 at Microsoft.Office.Server.Microfeed.SPMicrofeedThreadCollection.Populate(SPMicrofeedRetrievalOptions retrievalOptions, SPMicrofeedContext context)    
 at Microsoft.Office.Server.Microfeed.SPMicrofeedManager.CommonGetFeedFor(SPMicrofeedRetrievalOptions retrievalOptions)    
 at Microsoft.Office.Server.Microfeed.SPMicrofeedManager.CommonPubFeedGetter(SPMicrofeedRetrievalOptions feedOptions, MicrofeedPublishedFeedType feedType, Boolean publicView)    
 at Microsoft.Office.Server.Microfeed.SPMicrofeedManager.GetMyPublishedFeed(SPMicrofeedRetrievalOptions feedOptions, MicrofeedPublishedFeedType typeOfPubFeed, Boolean ShowPublicView)    
 at Microsoft.Office.Server.Social.SPSocialFeedManager.Microsoft.Office.Server.Social.ISocialFeedManagerProxy.ProxyGetFeed(SPSocialFeedType type, SPSocialFeedOptions options)    
 at Microsoft.Office.Server.Social.SPSocialFeedManager.<>c__DisplayClass4b`1.<S2SInvoke>b__4a()

However, I can successfully get every social feed by changing the first parameter in GetFeed() from Personal to Everyone.

How can I fix this?

Thanks,