Excel UDF 'not a valid addin' error

Question

I am trying to create a custom vb.net Excel 2007 function (UDF) using VS 2010 and have gotten to this stage (borrowing heavily from Eric Carter's example at http://blogs.msdn.com/b/eric_carter/archive/2004/12/01/273127.aspx):

Namespace AutomationAddin
    <Guid("1aeeb1b5-e099-4f7f-aeb0-3e9f19b64f62")>
    <ClassInterface(ClassInterfaceType.AutoDual)>
    <ComVisible(True)>
    Public Class MyFunctions
        Public MyFunctions()
        Public Function MultiplyNTimes(ByVal number1 As Double, ByVal number2 As Double, ByVal timesToMultiply As Double) As Double
            Dim result As Double = number1
            For i As Integer = 0 To timesToMultiply - 1
                result = result * number2
            Next
            Return result
        End Function
        <ComRegisterFunctionAttribute()>
        Public Shared Sub RegisterFunction(ByVal type As Type)
            Registry.ClassesRoot.CreateSubKey(GetSubKeyName(type, "Programmable"))
            Dim key As RegistryKey = Registry.ClassesRoot.OpenSubKey(GetSubKeyName(type, "InprocServer32"), True)
            key.SetValue("", (System.Environment.SystemDirectory + "\mscoree.dll"), RegistryValueKind.String)
        End Sub
        <ComUnregisterFunctionAttribute()>
        Public Shared Sub UnregisterFunction(ByVal type As Type)
            Registry.ClassesRoot.DeleteSubKey(GetSubKeyName(type, "Programmable"), False)
        End Sub
        Private Shared Function GetSubKeyName(ByVal type As Type, ByVal subKeyName As String) As String
            Dim s As System.Text.StringBuilder = New System.Text.StringBuilder
            s.Append("CLSID\{")
            s.Append(type.GUID.ToString.ToUpper)
            s.Append("}\")
            s.Append(subKeyName)
            Return s.ToString
        End Function
    End Class
End Namespace

However, when I build it using VS 2010 and try to load it in Excel 2007 using the Addin Manager>Automation I find it listed as AutomationAddin.AutomationAddin.MyFunctions and click OK only to get the error "AutomationAddin.AutomationAddin.MyFunctions is not a valid add-in." I have set the Build settings to Register for COM interop.

I've had a look online and tried following this article http://stackoverflow.com/questions/1506858/how-to-get-com-server-for-excel-written-in-vb-net-installed-and-registered-in-aut but to no avail. I checked my registry (after I built my project) and under CLSID/{myGuid}/InprocServer32/Default the data is set to C:\WINDOWS\system32\mscoree.dll and CLSID/{myGuid}/Programmable already exists.

I am not quite sure what I am doing wrong and would appreciate any guidance or suggestions on the topic.

Cheers,

Ben