My program runs fine, but there is a little problem. When I add new tracks previously existing file to the ListBox, the program experiences an error. The code seems unwilling to do looping in a new file which was added in a different time. Please help me. Thanks .... public partial class Form1 : Form { //... string[] files, paths; private void button1_Click(object sender, EventArgs e) { if (openFileDialog1.ShowDialog() == DialogResult.OK) { files = openFileDialog1.SafeFileNames; paths = openFileDialog1.FileNames; for (int i = 0; i < files.Length - 1; i++) { listBox1.Items.Add(files[i]); } } } private void listBox1_SelectedIndexChanged(object sender, EventArgs e) { axWindowsMediaPlayer1.URL = paths[listBox1.SelectedIndex]; } }