XSL Transform error in scripting functoid using external assembly

[David]

I succeed to add and connect a scripting funtoid in a map, specifying custom
script assembly, class and method from an external assembly in the same
solution.

Still, when running Test Map on a map using the method in my external
assembly, I receive the errors "Test Map failure" and
"XSL Transform error: Value cannot be null. Parameter name: extension"

Does this relate to...
1) The following hotfix?
"FIX: You receive an "XSL transform error" error message when you test a
map in BizTalk Server 2004 Mapper" (download missing)
http://support.microsoft.com/default.aspx?scid=kb;en-us;842495
http://www.webservertalk.com/message224830.html

2) Properties (like Me.ID = 6045) or dependencies of my external assembly
custom functoid class inheriting BaseFunctoid?

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/sdk/htm/ebiz_prog_map_mlnv.asp

3) Project references or studio environment?
I will reboot and restart the studio.
I will try to debug the functoid code by adding a debug process from a
parallell studio.

4) Something else?

( Please refer to http://www.webservertalk.com/message287817.html )
---
I have followed the recommended procedure (GAC, strong name, unique GUID,
hardcoded version)

--- Assembly.vb ---
<Assembly: Guid("629890A8-7503-45E1-9ACA-7B5CC7BB6D94")> <Assembly:
AssemblyVersion("1.0.0.0")>
<Assembly: AssemblyKeyFile("..\..\Functoids.snk")>

--- clsFunctoids.cb ---
Public Class Functoids
Inherits BaseFunctoid

Thank you for guiding me this far!
Looking forward to reading your answer on this one.

[David]

Problem solved:
1) Use the same strong name key for the external assembly as for the
orchestration.

2) Function names may not start with the "_" character
like "Public Function _MyFunction() as String"
(would make it appear on top of an alphabetically sorted dropdownlist)

Thank you.