Can you please refer to the answer in the support ticket that you have opened regarding the same issue: Ticket ID: 894222:
"When you initiate an insert, as you have noticed, there will be no items in the Items collection of the RadDataForm and you should use the InsertItem instead for calling the FindControl method. You can use the following code for handling both scenarios - the edit and insert:
(RadDataForm1.Items.Count > 0)
lblIdPlantaValor = (Label)RadDataForm1.Items.FindControl(
lblIdPlantaValor = (Label)RadDataForm1.InsertItem.FindControl(
If you have any further questions, I would suggest that we continue to conversation in the support ticket.