Set value of private field

Try this (inspired by Find a private field with Reflection?):

var prop = s.GetType().GetField("id", System.Reflection.BindingFlags.NonPublic
    | System.Reflection.BindingFlags.Instance);
prop.SetValue(s, "new value");

My changes were to use the GetField method - you are accessing a field and not a property, and to or NonPublic with Instance.

Evidently, adding BindingFlags.Instance seems to have solved it:

> class SomeClass
  {
      object id;

      public object Id
      {
          get
          {
              return id;
          }
      }
  }
> var t = typeof(SomeClass)
      ;
> t
[Submission#1+SomeClass]
> t.GetField("id")
null
> t.GetField("id", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
> t.GetField("id", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)
[System.Object id]
>