Problem in Searching UserObject Profile records in CS2007

Hi,

I am trying to search the records of UserObject profile by using the 
ProfileManagementContext class. I'm getting the error when i'm calling the

following code,
// Build dataset of searchable entities for a profile.
  DataSet searchableEntities  = profile.GetSearchableEntities();

// Build search clause for the UserObject.
  SearchClauseFactory factory = 
profile.GetSearchClauseFactory(searchableEntities, "UserObject");

 I'm getting the error message as follows,
System.ArgumentException: DataSet is missing the 'UserObject' table.
Parameter name: searchableEntities

Anybody can help me to solve this problem. 

Regards,
Mani