ASP.Net: How to clear an error

An Error Occured While getting Data From Hdr_AccountType.No mapping exists from object type System.Web.UI.WebControls.ListItem to a known managed provider native type.

protected void btnSave_Click(object sender, EventArgs e)
    {
        Int32 st;
        int len = browser.PostedFile.ContentLength;
        byte[] pic = new byte[len];
        browser.PostedFile.InputStream.Read(pic, 0, len);

        SqlCommand Cmd = new SqlCommand();
        SqlConnection Cnn = new SqlConnection();
        string ConnectionString;
        ConnectionString = ConfigurationManager.ConnectionStrings["PhotostudioConnectionString"].ConnectionString;

        Cnn.ConnectionString = ConnectionString;
        if (Cnn.State != ConnectionState.Open)
            Cnn.Open();
        Cmd.Connection = Cnn;
        Cmd.CommandType = CommandType.StoredProcedure;
        Cmd.CommandText = "sproc_Ins_ManualPhotoSettingsDetails";
        Cmd.Parameters.Clear();
        // Cmd.Parameters.AddWithValue("@Id", txtBillNo.Text);
        Cmd.Parameters.AddWithValue("@Name", txtName.Text);
        Cmd.Parameters.AddWithValue("@Phoneno", txtPhoneno.Text);
        Cmd.Parameters.AddWithValue("@Startdate", rdpDate.SelectedDate); 
        Cmd.Parameters.AddWithValue("@Enddate", rdpDelivDate.SelectedDate);
        Cmd.Parameters.Add("@Systemurl", SqlDbType.Image).Value = pic;
        SqlParameter Src = new SqlParameter("@FilePath", SqlDbType.NVarChar, 450);
        Src.Value = browser.PostedFile.FileName;
        Cmd.Parameters.Add(Src);
        Cmd.Parameters.AddWithValue("@Work", TextBox1.Text);
        Cmd.Parameters.AddWithValue("@Size", cmbSize.SelectedItem);
        Cmd.Parameters.AddWithValue("@Rate", txtRate.Text);
        Cmd.Parameters.AddWithValue("@Noofcopies", txtNoofcopies.Text);
        Cmd.Parameters.AddWithValue("@Total", txtTotal.Text);
        Cmd.Parameters.AddWithValue("@Paidamount", txtPaid.Text);
        Cmd.Parameters.AddWithValue("@Balance", txtbal.Text);



        try
        {
            st = Convert.ToInt32(Cmd.ExecuteScalar());

        }
        catch (Exception ex)
        {
            
            
            
                  
            
            throw new ApplicationException(
                "!!! An Error Occured While getting Data From Hdr_AccountType." + ex.Message);
            lblError.Visible = true;
            lblError.Text = "!!! An Error Occured While " + ex.Message.ToString();
            return;
        }



        Cmd.Dispose();