Marcel,
Seems like the ChildFormDialog issue you were having was resolved in the new release and VS had to update the references. If you put the assemblies into the GAC, the actual Version didn't change, only the File Version. So, the issues with VS/Fusion not updating the assembly used from the GAC would cause a problem.
Kinda like how you have to run your application twice in debug when you update the GAC assemblies in a post-build script for the new GAC assemblies to get used.
Anyway, I'm glad it's working for you now.