必须声明标量变量

执行到这里出现此错误：必须声明标量变量
catch (Exception ex)
{
throw ex;
}
整段代码：
/// <summary>
/// 添加用户
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void btselect_Click(object sender, EventArgs e)
{
SqlConnection cn = db.con();
string sqlyj = "select count(*) from users where 用户密码=@upsd and 用户编号=@uid";
SqlCommand cm = db.cm(sqlyj, cn);
cn.Open();

SqlParameter par2 = new SqlParameter("@upsd", SqlDbType.VarChar, 15);
par2.Direction = ParameterDirection.Input;
par2.Value = this.tbpsd.Text.Trim();

SqlParameter par1 = new SqlParameter("@uid", SqlDbType.Int);
par1.Direction = ParameterDirection.Input;
par1.Value = this.tbuid.Text.Trim();

SqlParameter[] s = { par1, par2 };
SqlCommand com=db.cm(sqlyj,cn );

//try
//{
int i = db.ExecuteNonQuery(sqlyj);
if (i <= 0)
{
MessageBox.Show("不存在该用户，请先注册！");
}
else
{
SqlDataAdapter da=new SqlDataAdapter ();
DataTable dt=new DataTable ();
da.Fill (dt);
}

那个 db.ExecuteNonQuery方法是调用这个：

public int ExecuteNonQuery(string str)
{
SqlCommand cm = new SqlCommand(str, connect);
try
{
int result = cm.ExecuteNonQuery();
return result;
}
catch (Exception ex)
{
throw ex;
}

必须声明标量变量-->是sql语句的问题，debug看下sql语句是什么，拿出去去sql分析器中调试好在放到代码中使用 节省时间

中@upsd和@uid两边加上 单引号