Eliminada la linea $this->idUser = $register['id_user']. En la tabla cofig no existe el campo id_user

classes/configuration.class.php

 				$register=$this->obtenerRegistro();
 				$this->tablePrefix = Table_prefix;
 				$this->urlGelato = $register['url_installation'];				
-				echo "<pre style='background-color:white;'>";
-				print_r($register);
-				echo" </pre>";
-			
-				$this->idUser = $register['id_user'];
 				$this->postLimit = $register['posts_limit'];
 				$this->title = $register['title'];
 				$this->description = $register['description'];