ASP.NET MVC 4 An exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll but was not handled in user code

Question

I'm using ASP.NET MVC4 When I'm trying to run my program that problem always pop up.

public class UsersService
{
    // Db Connection string
    string DBCon = ConfigurationManager.ConnectionStrings["DBCon"].ConnectionString;

    //View users list
    public List<UsersModel> All()
    {
        List<UsersModel> _UsersModel = new List<UsersModel>();

        using (SqlConnection conn = new SqlConnection(DBCon))
        {
            //call stored procedure
            using (SqlCommand cmd = new SqlCommand("GetUsers", conn))  
            {
                cmd.CommandType = System.Data.CommandType.StoredProcedure;

                conn.Open();

                SqlDataReader reader = cmd.ExecuteReader();

                while (reader.Read())
                {
                    UsersModel _UserModel = new UsersModel();
                    _UserModel.UserID = int.Parse(reader["UserID"].ToString());
                    _UserModel.Firstname = reader["Firstname"].ToString();
                    _UserModel.Middlename = reader["Middlename"].ToString();
                    _UserModel.Surname = reader["Surname"].ToString();
                    _UserModel.Email = reader["Email"].ToString();

                    _UsersModel.Add(_UserModel);
                }
            }
        }

        return _UsersModel;
    }
}

Answer 1

there is a problem with the connection to the database. The main reason for this... sorry, it could be a network issue, firewall, rejected port, wrong details, etc... What I would do: try try and catch to manage the exception and see the error that you are getting, For more info: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/try-catch