Code:
//in form login 
public partial class frmLogin : Form
    {
        private FormMain _frm;
        public frmLogin(FormMain frm)
        {
            InitializeComponent();
            _frm = frm;
        }

	 private void btnLogin_Click(object sender, EventArgs e)
        {
	
	bool CurrentLogin = false;
                CurrentLogin = Login(txtUserName.Text, txtPassword.Text);
...