Membership.ValidateUser always returns False

 Hi All,
          I have a code here, when i try to login,the validate user always returns false.
here is the code,
protected void btnSignIn_ServerClick(object sender, EventArgs e)
    {
      
        string MailId = txtMailId.Text.Trim();
        string Pwd = txtPwd.Text.Trim();

        MembershipUser objUsr = Membership.GetUser(MailId);
        if (objUsr != null)
        {
            lblMsg.Text = "Hi";//here i am getting the mailid(i.e same as UserName) correctly.
        }
        //objUsr.IsAppro ...