problem with AppDomain

I have have asked before about how to use the Appdomain to be able to load and unload Dll file and in the same time be able to pass arrays. And actually someone whom I thank a lot recommended me to use the AppDomain and he suggested to me the following code:

Public Class Form1

    Private FortranDomain As AppDomain
    Private FortranAgent As DomainAgent

    '1) Create the domain
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        FortranDomain = AppDomain.CreateDomain("Domain")
        FortranAgent = CType(FortranDomain.CreateInstanceAndUnwrap(GetType(DomainAgent).Assembly.GetName().FullName, _
                                                        GetType(DomainAgent).FullName), DomainAgent)
    End Sub


    '2) Use the methods in the domain agent
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        'Well, here the values are to be set right !!
        Dim IA() As Int32 = {1, 2, 3, 4, 5}
        Dim A() As Double = {}
        Dim IB() As Int32 = {1, 2, 3, 4, 5}
        Dim B() As Double = {}

        FortranAgent.oFortranDLL(A, IA)

        FortranAgent.oIntrFControl(B, IB)
    End Sub


    '3) Unload the domain and assemblies
    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        AppDomain.Unload(FortranDomain)
    End Sub

End Class



Friend Class DomainAgent : Inherits MarshalByRefObject

    Public Sub New()
    End Sub

    Public Sub oFortranDLL(ByRef A() As Double, ByVal IA() As Int32)
        FortranDLL(A, IA)
    End Sub

    Public Sub oIntrFControl(ByRef A() As Double, ByVal IA() As Int32)
        IntrFControl(A, IA)
    End Sub

    Private Declare Sub FortranDLL Lib "C:\Sams2000\Applications\ATTIF2000\Engine\ATTIFDLLENG.dll" Alias "FORTRANDLL" (ByRef A() As Double, ByVal IA() As Int32)
    Private Declare Sub IntrFControl Lib "C:\Sams2000\Applications\ATTIF2000\Engine\ATTIFDLLENG.dll" Alias "INTRFCONTROL" (ByRef A() As Double, ByVal IA() As Int32)
End the code can pass the arrays without any problems but the only problem come from
FortranAgent=CType(FortranDomain.CreateInstanceAndUnwrap(GetType(DomainAgent).Assembly.GetName().FullName,
 _ GetType(DomainAgent).FullName),
 DomainAgent)where the program will crash and give me the following attached error
I would like to thank the person who help me to have this code and I will be do appreciated if any one can help me to figure out what is the source
 of this problem
Many thanks
Ahmed