getting Node statistics : LocalLBNodeAdress.cs (SDK)

the probleem isn't due to the BIG-IP because the others informations are well displayed.

for example:

SESSION_STATUS_ENABLED

MONITOR_STATUS_UNCHEKED

Connection limit,ratio

...

I have just this exeption when i want to use "get_statistics" .Yes i'm using partitions(is it an other way tro proceed?)Perhaps it's just comming from the syntax :

////////////  
 NodeAddress.LocalLBNodeAddressNodeAddressStatistics statistics =  
                 NodeAddress.get_statistics(node_list);  
    
    
 for (int i = 0; i < node_list.Length; i++)  
 {  
 NodeAddress.CommonStatistic[] statistic_list = statistics.statistics[ i ].statistics;  
   for (int j = 0; j < statistic_list.Length; j++)  
      {  
       Console.WriteLine("                       " +  
       statistic_list[ j ].type.ToString() + " : " + build64(statistic_list[ j ].value));  
      }  
 }

PS: Thx for your help and excuse my english. i'm french