Hi
In fact the problem seems related to multi-site management.
I
 had created a subdomain for my future forum, I just deactivated it to 
test but I realized that the variable in the method did not change so I 
modified to test the condition if below.
And it works.
Below the code.
// onAfterInitialise
   public function onAfterInitialise()
   {
     $app   =   JFactory::getApplication();
     if ( $this->restapi ) {
       $format     =   JCckWebservice::getConfig_Param( 'resources_format', 'json' );
       $path     =   JUri::getInstance()->getPath();
       $segment   =   substr( $path, strrpos( $path, '/' ) + 1 );
       if ( $segment != '' ) {
         if ( ( $pos = strpos( $segment, '.' ) ) !== false ) {
           $format   =   substr( $segment, $pos + 1 );
           if ( $format[0] == 'w' ) {
             $format   =   substr( $format, 1 );
           }
         }
       }
       
       $app->input->set( 'format', $format );
     }
     if ( $app->isSite() ) {
       $router   =   JCck::on( '3.3' ) ? $app::getRouter() : $app->getRouter();
       $router->attachBuildRule( array( $this, 'buildRule' ) );
     } elseif ( $app->isAdmin() && $app->input->get( 
'option' ) == 'com_config' && strpos( $app->input->get( 
'component' ), 'com_cck' ) !== false ) {
       JFactory::getLanguage()->load( 'com_cck_core' );
     }
     
     if ( JCckToolbox::getConfig()->get( 'processing', 0 ) ) { // todo: move below
       JCckToolbox::process( 'onAfterInitialise' );
     }
     if ( $this->multisite !== true ) {
       return;
     }
return;
It  work's
Of course it's for the test, I wait for your answer.
Regard's