Operation could destabilize the runtime error when invoke ToString from int using Emit

This code works

var toString = typeof(string).GetMethod("ToString", new Type[] { });

var dm = new DynamicMethod("MyToString", typeof(string), new Type[] { typeof(string) });

var il = dm.GetILGenerator();

il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Callvirt, toString);
il.Emit(OpCodes.Ret);

Delegate d = dm.CreateDelegate(typeof(Func<string, string>));

var r = d.DynamicInvoke("10");

This code throws an exception (System.Security.VerificationException: Operation could destabilize the runtime.)

var toString = typeof(int).GetMethod("ToString", new Type[] { });

var dm = new DynamicMethod("MyToString", typeof(string), new Type[] { typeof(int) });

var il = dm.GetILGenerator();

il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Callvirt, toString);
il.Emit(OpCodes.Ret);

Delegate d = dm.CreateDelegate(typeof(Func<int, string>));

var r = d.DynamicInvoke(10);

why?