Thanks for your offer Stefan, I did not see my post was published earlier. In fact, I created another (identical) project, and it all went just fine. Don't know what happened, maybe some initialisation when i used the project template for the first time?
Anyway, VB works and it's fun to use it for Netduino, as I am now more familiar with it than with C#, due to my job.
Do a simple windiff on the VBproj files to see if there is any obvious differences.