class Tx_SimpleOrders_Domain_Model_File extends TYPO3CMSExtbaseDomainObjectAbstractEntity {

    ...
}

class Tx_SimpleOrders_Controller_FileController extends TYPO3CMSExtbaseMvcControllerActionController {

    public function showAction() {

        echo "<pre>";
        var_dump( class_exists('Tx_SimpleOrders_Domain_Model_File') );
        echo "</pre>";

    }



    /**
     * Creates a new file
     *
     * @param Tx_SimpleOrders_Domain_Model_File $newFile A fresh File object which has not yet been persisted
     * @return void
     */
    public function createAction(Tx_SimpleOrders_Domain_Model_File $newFile) {

        echo "<pre>";
        var_dump($_POST["tx_simpleorders_upload"]["newFile"]);
        echo "</pre>";

    }


}

The argument type for parameter $newFile of method Tx_SimpleOrders_Controller_FileController->createAction() could not be detected.

{namespace so=Tx_SimpleOrders_ViewHelpers}

<f:form enctype="multipart/form-data" method="post" controller="File" action="create" name="newFile" object="{newFile}">

  <f:form.textfield property="identifier" /><br />
  <f:form.textarea property="description" rows="3" cols="40" /><br />
  <!--<f:form.upload property="image" /><br />-->
  <f:form.submit class="submit" value="Hochladen" />

</f:form>