@christian.stan it should still work as my example does in Dynamo 2.17. Do you happen to have a package installed that also has a “Surface” class? If so, you’ll need to fully qualify the namespace or Dynamo doesn’t’ know which one you refer too.
Can it be from the built-in packages (more intellectual curiosity)
You gave me a solution, thanks.
cordially
christian.stan
It can be from any package at all, yes 
If you have a namespace conflict, it should show up when you try to write in the Code Block as an option in the intellisense.
Assuming you’re testing in sandbox?
I believe that Revit implemented a surface class in 2022 (i think) for their analytical surfaces, causing a namespace conflict.