It works. There are no compatibility issues. You've done something wrong, but I'm not sure what.
Please post the entire compilation trace - not just the error.
Re: software problem with Playground Express
Re: software problem with Playground Express
Re: software problem with Playground Express
And as far as I can see it does not claim to be.the CircuitPlaygroundExpress is not really Arduino Compatible.
Re: software problem with Playground Express