Problem to Create Custom String Aggregate Function for GridView

Dear All,

I am using Telerik Silverlight UI Control.

Once i has Create Custom Aggegate function for Number Type and Its working Fine but Now I needed String Aggegate function Code are Following.

Code :

  public class RPT_CustomAggregates_Function : EnumerableSelectorAggregateFunction
    {
        protected override string AggregateMethodName
        {
            get
            {
                return "RPT_CustomAggregates";
            }
        }

        protected override Type ExtensionMethodsType
        {
            get
            {
                return typeof(Statistics);
            }
        }
    }

 public static class Statistics
    {
        public static object RPT_CustomAggregates<T>(IEnumerable<T> source, Func<T, object> selector)
        {
            return "Hello";
        }
}

This Code give Error on runtime. 

No generic method 'RPT_CustomAggregates' on type 'Report_Config.Statistics' is compatible with the supplied type arguments and arguments. No type arguments should be provided if the method is non-generic.

 Please guide how to resolve this problem.

Thanks,

Jignesh