IronPython Excel-Dna加载项 - 关于Microsoft.Dynamic引用的例外

pyEngine.Runtime.LoadAssembly(myclass); 

/*
Added these references all as Local Copies - probably not necessary?

System.Windows.Forms
Microsoft.CSharp

ExcelDna.Integration (from Excel-DNA distribution folder)
IronPython (from IronPython folder)
IronPython.Modules (from IronPython folder)
Microsoft.Dynamic (from IronPython folder)
Microsoft.Scripting (from IronPython folder)
Microsoft.Scripting.Metadata (from IronPython folder)

mscorlib (I don't really know why I added this, but it was one of the references in my IronPython class library)

MyClass (this is the reference to my IronPython class - I checked to see that it gets copied in every time I rebuild the solution and it does)

These were automatically added by SharpDevelop when I created the project.
System
System.Core
System.Windows.Forms
System.Xml
System.Xml.Linq
*/
using System;
using System.IO;
using System.Windows.Forms;
using ExcelDna.Integration;
using System.Reflection;
using IronPython.Hosting;
using Microsoft.Scripting.Hosting;

public class MyAddIn : IExcelAddIn
{
    public void AutoOpen()
    {
        try
        {
            string xllDirectory  = Path.GetDirectoryName(@"C:/Users/myname/Documents/SharpDevelop Projects/IronPythonExcelDNATest/MyAddIn/bin/Debug/");
            string dllPath = Path.Combine(xllDirectory,"MyClass.dll");
            Assembly myclass = Assembly.LoadFile(dllPath);
            ScriptEngine pyEngine = Python.CreateEngine();
            pyEngine.Runtime.LoadAssembly(myclass);
            ScriptScope pyScope = pyEngine.Runtime.ImportModule("MyClass");
            object myClass = pyEngine.Operations.Invoke(pyScope.GetVariable("MyClass"));
            IronTest.AddSomeStuff = pyEngine.Operations.GetMember<Func<double, double,double>>(myClass, "AddSomeStuff");
        }
        catch (Exception e)
        {
            MessageBox.Show(e.ToString());
        }
    }
    public void AutoClose()
    {
    }
}

public class IronTest
{
    public static Func<double, double, double> AddSomeStuff;
    public static double TestIPAdd(double val1, double val2)
    {
        try
        {
            return AddSomeStuff(val1, val2);
        }
        catch (Exception e)
        {
            MessageBox.Show(e.ToString());
            return double.NaN;
        }
    }
}

class MyClass:
    def __init__(self):
        pass

    def AddSomeStuff(self,x,y):
        return x + y