Ошибка CS0120 Для нестатического поля, метода или свойства “LectureForm.btnNext” требуется ссылка на объект(2)

код Param:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
namespace Victorina
{
    public partial class Param : Form
    {
        private LectureForm lectureForm;
        public Param(LectureForm lectureForm)
        {
            InitializeComponent();
            this.lectureForm = lectureForm;
        }
        public Param()
        {
        }
        private void Param_Load(object sender, EventArgs e)
        {
            listBox1.Items.Clear();
            listBox1.Items.AddRange(Victorina.list.ToArray());
            checkBox1.Checked = true;
        }
        private void btnSelectFolder_Click_1(object sender, EventArgs e)
        {
            FolderBrowserDialog fbd = new FolderBrowserDialog();
            if (fbd.ShowDialog() == DialogResult.OK)
            {
                string[] video_list = Directory.GetFiles(fbd.SelectedPath, "*.mp4", SearchOption.AllDirectories);
                Victorina.lastFolder = fbd.SelectedPath;
                listBox1.Items.Clear();
                listBox1.Items.AddRange(video_list);
                Victorina.list.Clear();
                Victorina.list.AddRange(video_list);
            }
        }
        private void btnClearList_Click(object sender, EventArgs e)
        {
            listBox1.Items.Clear();
        }
        private void btnOK_Click_1(object sender, EventArgs e)
        {
            Victorina.WriteParam();
            this.Hide();
        }
        private void btnCancel_Click_1(object sender, EventArgs e)
        {
            this.Hide();
        }
        public void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
            if (checkBox1.Checked == true)
            listBox1.Visible = true;
            checkBox2.Checked = false;
            listBox2.Visible = false;
            lectureForm.btnNext.Visible = true;
            lectureForm.WMP.Visible = true;
        }
        private void checkBox2_CheckedChanged(object sender, EventArgs e)
        {
        }
    }
}
код LectureForm:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Victorina
{
    public partial class LectureForm : Form
    {
        public LectureForm()
        {
            InitializeComponent();
        }
        public void btnNext_Click(object sender, EventArgs e)
        {
            WMP.URL = Victorina.list[1];
        }
        private void LectureForm_Load(object sender, EventArgs e)
        {
        }
        private void btnTest_Click(object sender, EventArgs e)
        {
            TrafficLawsApp.TestController.Start();
            this.Hide();
        }
    }
}