Cannot Access File

 private void button1_Click(object sender, EventArgs e)
        {
           
            //try {
            //    StreamReader str = new StreamReader("D:\\account.txt");
            //    while (true)
            //    {
            //        String line = str.ReadLine();
            //        if (line == null) { str.Close(); break; }
            //        String[] word = line.Split(',');
            //        user = word[0];
            //        pass = word[1];
            //        if (textBox1.Text == user && textBox2.Text == pass)
            //        {
            //            str.Close();
            //            Form1 f1 = new Form1();
            //            f1.Show();
            //            this.Hide();
            //            break;
            //        }
            //        else
            //        {
            //            MessageBox.Show("wrong data");
            //            this.Hide();

            //        }

            //    }
               
               
               
            //}
            //catch(FileNotFoundException){MessageBox.Show("not found");}
            Form1 f1 = new Form1();
            f1.Show();
            this.Hide();
       }
 

 Error	1	Unable to copy file "obj\x86\Debug\SeglMadanyProject.exe" to "bin\Debug\SeglMadanyProject.exe". The process cannot access the file 'bin\Debug\SeglMadanyProject.exe' because it is being used by another process.	SeglMadanyProject