"Error" loading date

Question

I have a screen whose a certain "Reference Date" field receives the next available date of a file, following the dates that are in the database.

On the field side I have a "Calendar" icon that when triggered should load the calendar.

Well, I don’t know what’s going on, it doesn’t return the next date and it doesn’t load the calendar, I’m not seeing errors in the code.

"Reference Date" > txtDataArchive

Periodicity and date check = "Verifiedavailable(ds)"

Calendar action > "dpbDataArchive"

    if (ds.Tables[0].Rows[0]["DATELASTARCHIVE"] != DBNull.Value && ds.Tables[0].Rows[0]

     ["PERIODICIDADE"].ToString().Equals("0"))
        {
            this.txtDataArchive.Visible = false;

            this.dpbDataArchive.Visible = false;

            this.ddlDataPub.Visible = true;

            VerificaDataDisponivel(ds);
        }


  //Método VerificaDataDisponivel(ds)

   DataTable dtDataDisponivel = new DataTable("DataDisponivel");

        dtDataDisponivel.Columns.AddRange(new System.Data.DataColumn[] {new DataColumn("COD_DATA"), new DataColumn("DSC_DATA")});

        DataRow drData = null;
        bool flgFimCalendario = false;

        //Verify the possible dates 
        BO.Feriado feriado = new BO.Feriado();
        DataSet dsQuantArquPasta = BO.Pasta.BuscarQuantidadeArquivoPasta(this.CodPasta);

        DateTime dtul = DateTime.MinValue;
        //DateTime dtfimperio = DateTime.MinValue;

        int tipoPeriodicidade = Convert.ToInt32(ds.Tables[0].Rows[0]["TipoPeriodicidade"]);

        if(ds.Tables[0].Rows[0]["DATELASTARCHIVE"] != DBNull.Value)
        {
            dtul = (DateTime)ds.Tables[0].Rows[0]["DATELASTARCHIVE"];
        }