类型为system . formatexception的未处理异常;输入字符串格式不正确

我目前正在学习c#，我正试图让我的头围绕类继承，并写了一些代码来显示一行到控制台，但我在这个帖子主题中遇到了错误问题。

在字符串的子类PC中抛出错误。行格式。我假设它与我传递的类型有关，但到目前为止，我所尝试的一切都不起作用。任何输入都是非常感谢的，因为我想确保在我进入下一个训练之前我完全理解了这一点。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ClassInheritance
{
    class Program
    {
    static void Main(string[] args)
    {
        PC myPC = new PC();
        myPC.casetype = "Black SuperCool";
        myPC.contract = true;
        myPC.dateadded = DateTime.Now;
        myPC.id = 1;
        myPC.type = "Small form factor";
        printEquipmentDetails(myPC);
        Console.ReadLine();
    }
    private static void printEquipmentDetails(Equipment Equipment)
    {
        Console.WriteLine("Details: {0}", Equipment.DisplayEquipment());
    }
}
abstract class Equipment
{
    public int id { get; set; }
    public string type { get; set; }
    public bool contract { get; set; }
    public DateTime dateadded { get; set; }
    public abstract string DisplayEquipment();
}
class PC : Equipment
{
    public string casetype { get; set; }
    public override string DisplayEquipment()
    {
        return String.Format("(0} - {1} - {2} - {3} - {4}", this.id, this.type, this.contract.ToString(), this.dateadded.ToShortDateString(), this.casetype);
    }
}
class Laptop : Equipment
{
    public string batterylife { get; set; }
    public override string DisplayEquipment()
    {
        return String.Format("(0} - {1} - {2} - {3} - {4}", this.id, this.type, this.contract, this.dateadded, this.batterylife);
    }
}
}