Does a guide for installation of drupal Cartaro distribution exist?
Have a look at Cartaro's Getting Started guide. Especially see the quoted commands to set up permissions for PostGIS properly.

Additionally, there have been changes to the error reporting of Cartaro in July which should result in more precise error messages in case something is wrong with PostGIS.

Please report any bugs in Cartaro using its bug tracker on the Drupal site so that is does not get overlooked. We'd be happy to see a report there regarding the GeoServer terminology along with a more verbose description.