executeScalar method is giving error

Hi All,

public string execCount(string query)
        {
            string CS = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
            using (SqlConnection con = new SqlConnection(CS))
            {

                SqlCommand cmd = new SqlCommand(query,con);
               cmd.Connection = con;
                string count = cmd.ExecuteScalar().ToString();
               

                return count;
            }
        }

It is giving me error saying that 

ExecuteScalar requires an open and available Connection. The connection's current state is closed. What is the error here?

Thanks