Function SumLookup(ByVal items As Object()) As Decimal
If items Is Nothing Then
Return Nothing
End If
Dim suma As Decimal = New Decimal()
Dim ct as Integer = New Integer()
suma = 0
ct = 0
For Each item As Object In items
suma += Convert.ToDecimal(item)
ct += 1
Next
If (ct = 0) Then return 0 else return suma
End Function

=Code.SumLookup(LookupSet(Fields!sJerarquiaNivel2.Value,Fields!Unidad.Value,Sum(Fields!InventarioSobreVentas.Value, "DS_DataInventarioDosAniosAnterior"))