TYPO3: The default controller for extension and plugin can not be determined.

We have an extension called typext

in model we have

    class Typext{
        ... get set methods ...


in TypextController.php

    namespace TYPO3\Typext\Controller; 

    class TypextController extends \TYPO3\CMS\Extbase\Mvc\Controller\ActionController{

    public function listAction(){

in ext_localconf.php

    'TYPO3.' . $_EXTKEY,
    array('Typext' => 'list,single,display,update,save')

in ext_tables.php

    'Description for Plugin'
 $pluginSignature = str_replace('_','',$_EXTKEY) . '_typext';

We have everything right and still we get an error. 

Suppose we have used some other plugin that has a flexform, and we have configured it.
But later we edited the same content element and replaced the existing plugin with the plugin from our extension 'typext'.
Now we do not see any flexform configuration here, but still in database the flexform from old plugin is saved.
This leads to the above mentioned error.


Add a new content element or edit the content element in database and remove the flexform content from the database.