Remove your AmetysHome directory

In the web template, edit the file webapp\cms\plugins\default-ud\content-types\org.ametys.plugin.defaultud.Content.uduser.xml and extends an unexisting extension 

 <cms:content-type extends="UNEXISTING">

Start Ametys > Configuration required

Fill the configuration > Restart

An error occurred about the UNEXISTING content type

Repair the error

Restart Ametys 

Every thing should be fine by now, but we have

org.ametys.core.migration.MigrationException: Your existing repository does not support automatic migrations (ametys:versions does not exist). Please follow the migration guide.