Installing SonataAdminBundle Error

If you get the next error when installing SonataAlbumBundle:

The child node "default_contexts" at path "sonata_block" must be configured.

Then you should include this code in your app/config/config.yml file

 # app/config/config.yml
sonata_block:
    default_contexts: [cms]
    blocks:
        sonata.admin.block.admin_list:
            contexts:   [admin]

        #sonata.admin_doctrine_orm.block.audit:
        #    contexts:   [admin]

        sonata.block.service.text:
        sonata.block.service.action:
        sonata.block.service.rss:

        # Some specific block from the SonataMediaBundle
        #sonata.media.block.media:
        #sonata.media.block.gallery:
        #sonata.media.block.feature_media:

Reference http://sonata-project.org/bundles/block/master/doc/reference/installation.html