The problem was that one!
If I write
Nome_Dos_Formadores <- rbind(V_Nome_Dos_Formadores, N_Nome_Dos_Formadores)
instead of
Nome_Dos_Formadores <- rbind(V_Nome_Dos_Formadores$`Nome do Formador`, N_Nome_Dos_Formadores$`Nome do Formador`)
it works fine. Thank you for your help!