Clean build - 70% of the time, it solves the problem every time. We'd like to understand every problem before solving, but sometimes it's just easier start with a clean slate and see if that works. So if you're using IntelliJ and maven, here is how to do that. Make sure you have no suspicious changes in your workspace. If you want to be really through, you can delete this directory, in order to make maven get all dependencies anew... full post»