"Operation could destablize the runtime" and DynamicMethod with value types

Question

I'm trying to generalize the following IL (from Reflector):

.method private hidebysig instance void SetValue(valuetype Test.TestFixture/ValueSource& thing, string 'value') cil managed
{
    .maxstack 8
    L_0000: nop 
    L_0001: ldarg.1 
    L_0002: ldarg.2 
    L_0003: call instance void Test.TestFixture/ValueSource::set_Value(string)
    L_0008: nop 
    L_0009: ret 
}

However, when I try and reproduce this IL with DynamicMethod:

     [Test]
 public void Test_with_DynamicMethod()
 {
  var sourceType = typeof(ValueSource);
  PropertyInfo property = sourceType.GetProperty("Value");

  var setter = property.GetSetMethod(true);
  var method = new DynamicMethod("Set" + property.Name, null, new[] { sourceType.MakeByRefType(), typeof(string) }, true);
  var gen = method.GetILGenerator();

  gen.Emit(OpCodes.Ldarg_1); // Load input to stack
  gen.Emit(OpCodes.Ldarg_2); // Load value to stack
  gen.Emit(OpCodes.Call, setter); // Call the setter method
  gen.Emit(OpCodes.Ret);

  var result = (SetValueDelegate)method.CreateDelegate(typeof(SetValueDelegate));

  var source = new ValueSource();

  result(ref source, "hello");

  source.Value.ShouldEqual("hello");
 }

 public delegate void SetValueDelegate(ref ValueSource source, string value);

I get an exception of "Operation could destabilize the runtime". The IL seems identical to me, any ideas? ValueSource is a value type, which is why I'm doing a ref parameter here.

EDIT

Here's the ValueSource type:

     public struct ValueSource
 {
  public string Value { get; set; }
 }

Answer 1

Change the args to 0/1 (not 1/2):

    gen.Emit(OpCodes.Ldarg_0); // Load input to stack
    gen.Emit(OpCodes.Ldarg_1); // Load value to stack

because the dynamic method it seems to be created as static, not instance (your original method is instance) - hence the args are off by one.

(sorry for the original wrong answer - you can leave the other bit of code as true)