Invoke member through reflection passing derived class as argument

I'm trying to call the method 'MyMethod' of class 'CMyClass'. This method has a parameter of type "CBaseClass", and I'm passing an object of type "CDerivedClass".

Class CBaseClass
    Public m_AMember As String
    Sub MethodOne()
        // DoSomething
    End Sub
End Class

Class CDerivedClass
    Inherits CBaseClass
    Public m_MyMember As Integer
    Sub MethodTwo()
        // DoSomething
    End Sub
End Class

Class CMyClass
    Sub MyMethod(ByVal obj As CBaseClass)
        // DoSomething
    End Sub
End Class

Sub Main()
    'load assembly
    Dim objAssembly As Assembly = Assembly.LoadFrom("myfile.dll")

    'create class instance and MethodInfo object
    Dim t As Type = objAssembly.GetType("MyNamespace.CMyClass")
    Dim obj As Object = Activator.CreateInstance(t)
    Debug.Assert(obj IsNot Nothing)
    Dim m As MethodInfo = t.GetMethod("MyMethod")
    Debug.Assert(m IsNot Nothing)

    'Init arguments (only one)
    Dim par As New CDerivedClass()
    Dim parameters As Object() = New Object(0) {par}

    'invoke method
    m.Invoke(obj, parameters) '<<<< ArgumentException here!
End Sub

The argument exception says "object of type 'MyNamespace.CDerivedClass' cannot be converted to type 'MyNamespace.CBaseClass'.

I changed "ByRef" to "ByVal" in MyMethod signature, but nothing changed. I tried to change type of 'par' object with:

Dim par As CBaseClass = New CDerivedClass()

without success. How I can invoke correctly the method "MyMethod" with an instance of derived class? Thank you very much.