C#登陆失败，至少一个参数没有被指定值，求帮助

Question

private void 管理员ToolStripMenuItem_Click(object sender, EventArgs e)
{
string uid = null; //初始化登录名
string pwd = null; //初始化登陆密码
Login lg = new Login(this); //创建登陆对话框
lg.ShowDialog(); //显示登陆对话框
uid = lg.uid; //获取登录名
pwd = lg.pwd; //获取登陆密码
cmd.CommandText = "select count(*) from ManagerLogin where 用户名='" + uid + "'and 密码='" + pwd + "'";

if ((int )cmd .ExecuteScalar () >0 ) //判断登录名和密码
{
MessageBox.Show("登陆成功");
panel1.Visible = true;
toolStripMenuItem1.Enabled = true;
pictureBox1.Visible = false;
textBox1.Visible = false;

        }

if ((int )cmd .ExecuteScalar () >0 )这里报错,至少一个参数没有被指定值。
我是初学者，希望大神多指点，帮忙解决下，拜托了！