System.TypeLoadException when calling a Sub()

[Treval]

Good day.

Here's my problem:

http://www.valter.be/other/problem.txt

I don't know what's going on.

I have tried completely removing everything and starting the projects over from scratch, but I get the same errror. I'm on a deadline here...

What I did:
project -> properties -> general -> outpit type = class library

GUI properties -> startup object: GUI

GUI -> References -> add -> projects -> select Dieren

import Dieren

solution -> single startup object -> GUI

Any help is greatly appreciated.

Treval