error al actualiar de 3.8.4 a 4.1.x

pues que he seguido todos los pasos para actualizar mi foro y me ha saltado este error al ir a intentar abrir el upgrade.php en el explorador y no hay forma de seguir palante a ver si me podeis hechar una mano, gracias de antemano


Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@aquaforum.es and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.