TypeError when editing ressources

I am Using Ckan 2.10.1 and just installed ckanext-validation. I have linked the required presets and the required presets
`scheming.dataset_schemas = ckanext.validation.examples:ckan_default_schema.json
scheming.presets = ckanext.scheming:presets.json
Ckanext.validation:presets.json
`
Now when I click on an existing resource and even when I am not changing anything but clicking on "Update resource" I get this error:
`TypeError: str cannot be used as validator because it is not a user-defined function`. Why is that and how can I fix this? I am quite new to the ckan world and it's also the first time working for me with ckanext-validation so maybe I am just missing something I don't know. Any help is much appreciated, thanks in advance!