When usieing StofDoctrineExtensions (which is a Symfony2 port of Gedmo Doctrine Extensions) Sortable behaviour I kept on getting this error:
This repository can be attached only to ORM sortable listener
Since I could not easily find the answer in official docs I'm leaving an answer here for future reference.
You need to enable any listeners you are using. In this case, Sortable.
stof_doctrine_extensions:
default_locale: en_US
orm:
default:
sortable: true
For Symfony 4, add this configuration in /config/packages/stof_doctrine_extensions.yaml. For older versions of Symfony, add it to config.yml.