To recreate: 1. Have a plugin 2. Add a new method to it 3. Install the new plugin, or in k-t-d just update your code. 4. You will get 500 errors: Plugin does not have method configure at /usr/share/koha/lib/Koha/Plugins/Handler.pm line 73. 5. Run install_plugins.pl. 6. Now the plugin works.