I can´t update a rec

I can´t update a rec

I am trying to update a rec with the following script

recibo = Recibo_de_Caf[N_mero_de_Recibo_ == input.Recibo_de_Caf.toString()];
recibo.Estado_="Anulado";

But when I "run" the app it show me the following message:



What is the problem, What am I doing wrong.