Erro de Login com MySQL

public static void login (clsLogin log, frmPrincipal principal)
        {
            using(MySqlConnection conexaoMySQL = clsBanco.getInstancia().getConexao())
            {
                try
                {
                    
                    string mSQL = "SELECT count(*) FROM USUARIOS WHERE USUARIO=@usuario AND SENHA=@senha";
                    MySqlCommand cmd = new MySqlCommand(mSQL, conexaoMySQL);
                    cmd.Parameters.Add("@usuario",MySqlDbType.VarChar).Value = log.Usuario;
                    cmd.Parameters.Add("@senha", MySqlDbType.VarChar).Value = log.Senha;
                    conexaoMySQL.Open();
                    int i = (int)cmd.ExecuteScalar();

                    if (i > 0)
                    {
                        principal.Enabled = true;
                        principal.Show();
                    }
                    else
                    {
                        MessageBox.Show("Usuario/Senha estão inválidos.", "Alerta", MessageBoxButtons.OK, MessageBoxIcon.Question);
                    }

                    }
                catch (FbException ex)
                {
                    throw ex;
                }
                finally
                {
                    conexaoMySQL.Close();
                }
            }

private void btnEntrar_Click(object sender, EventArgs e)
        {
            
            try
            {
                clsLogin login = new clsLogin();
                frmPrincipal p = new frmPrincipal();
                login.Usuario = txtUsuario.Text;
                login.Senha = txtSenha.Text;
                clsBanco.login(login, p);
                p.Label(txtUsuario.Text);

                if (p.Enabled == true)
                {
                    Visible = false;
                }
                else
                { 
                
                }
            }

            catch (Exception erro)
            {
                MessageBox.Show("Erro de conexão com banco de dados" + erro.Message, "Alerta", MessageBoxButtons.OK, MessageBoxIcon.Question);
            }
        }