Android/Eclipse: Project 'MyProject' is missing required source folder: 'gen'

I'm having lots of problems with my Eclipse (when I'll solve them I'll write about it).

Anyhow, after creating a new project in a new workspace I get the following error:
Project 'MyProject' is missing required source folder: 'gen'
After building the project there's a second error:
The project cannot be built until build path errors are resolved

A temporary solution: in the Package Explorer delete gen folder. Rebuilding the project again will fix the problem. Why it's temporary? you'll have to do it with every new project.