The single-table inheritance mechanism failed to locate the subclass
ActionView::Template::Error (The single-table inheritance mechanism failed to locate the subclass: 'EpmEasyButtons'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this column if you didn't intend it to be used for storing the inheritance class or overwrite EasyPageModule.inheritance_column to use another column for that information.)
Don't directly delete plugin files, plugins must be correctly uninstalled before that. Use:
bundle exec rake easyproject:uninstall:all_plugins RAILS_ENV=production
for easy plugins (the plugin will be unmigrated and removed)
bundle exec rake redmine:plugins:migrate RAILS_ENV=production VERSION=0 NAME=redmine_agile
for redmine plugins (after that it's safe to remove plugin files).
If you don't have plugin files anymore or there is an error in migrations. You can delete non-existing entries manually in the rails console (rails c production):
raises an error
ActionView::Template::Error (The single-table inheritance mechanism failed to locate the subclass: 'EpmEasyButtons')
EasyPageModule.where(:type => 'EpmEasyButtons').delete_all
repeat until there is no error.
the same error can appear on all tables with inheritance columns - EasyPageModule, EasyQuery, CustomField, EasyRakeTask, Attachment etc.