Hi H,
Deleting the package instance from Sitemap -> "Unmounted Applications" will not work. (At least it did not work for me).
What worked was to delete ALL News instances (and eventual customized code - so save a copy of it if this is the case). To do this, go to /acs-admin/apm/, click on one of the News links in the table of packages and on the next page click on the "Delete this package from your system" link at the bottom. But be very careful (as is stated loud and clear) as this will delete packages/news from your disk.
