Dear Eduardo,
guess the error message comes from the prototype page "news". Actually, the upgrade scripts are supposed to add new revision to the instantiated prototype pages. In case, something went wrong, you can reload the prototype page via ds/shell (assuming the instance is called /xowiki, and the problem comes from the "news" prototype page
::xowiki::Package initialize -url /xowiki
$package_id import-prototype-page news
Hope, this helps
