Howdy arturbarrera!
Google is currently reporting an error with generating your Knol export file and we could not download it.
Google Takeout might have more details on the status of your export and you might be able to download it from https://www.google.com/takeout/#download
If all seems well there, you can try to import again by signin-in with your existing WordPress.com account and selecting the blog you had intended to import to.
If you are stil having issues, please contact support: http://en.support.wordpress.com/contact/?partner=knol
Blog url: http://arturbarrera.wordpress.com/
markel