Buenos días Redlo,
1. El valor numérico de los permisos de archivo es el “666”. El resto de “casillas” (permisos de propietario, grupo y públicos) están activadas para leer y escribir, pero no lo están para ejecutar.
2. He escrito una frase cualquiera en configuration.php. Lo he guardado, he cerrado el fllezilla, lo he vuelto a abrir, he reabierto el archivo y los cambios continuaban allí.
3. He ido descubriendo que 1&1 tiene un muy buen servicio de márqueting pero un pésimo servicio técnico. Volveré a llamarles y escribirles, aunque ya no sé muy bien que decirles o que pueden hacer ellos…

Muchas gracias por tu respuesta Redlo,
El problema persiste. Puedo escribir en el archivo .htaccess. He hecho lo que me has indicado, tanto en el propio archivo como en la “configuración global”. Siempre me reescribe la URL. Es decir, por ejemplo: http://www.enavales.com/e-noticias. También he probado de ponerle y quitarle el # antes del “Options +FollowSymLinks” y del RewriteBase /index.php. Pero en cualquier caso, me continúa saliendo el mismo error:

[i]”Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, 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 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.”[/i]

Ahora mismo el .httacces que tengo después de renombrar el htaccess.txt es:

##
# @package Joomla
# @copyright Copyright (C) 2005 – 2014 Open Source Matters. All rights reserved.
# @license GNU General Public License version 2 or later; see LICENSE.txt
##

##
# READ THIS COMPLETELY IF YOU CHOOSE TO USE THIS FILE!
#
# The line just below this section: ‘Options +FollowSymLinks’ may cause problems
# with some server configurations. It is required for use of mod_rewrite, but may already
# be set by your server administrator in a way that dissallows changing it in
# your .htaccess file. If using it causes your server to error out, comment it out (add # to
# beginning of line), reload your site in your browser and test your sef url’s. If they work,
# it has been set by your server administrator and you do not need it set here.
##

## Can be commented out if causes errors, see notes above.
Options +FollowSymLinks

## Mod_rewrite in use.

RewriteEngine On

## Begin – Rewrite rules to block out some common exploits.
# If you experience problems on your site block out the operations listed below
# This attempts to block the most common type of exploit `attempts` to Joomla!
#
# Block out any script trying to base64_encode data within the URL.
RewriteCond %{QUERY_STRING} base64_encode[^(]*([^)]*) [OR]
# Block out any script that includes a tag in URL.
RewriteCond %{QUERY_STRING} (|%3E) [NC,OR]
# Block out any script trying to set a PHP GLOBALS variable via URL.
RewriteCond %{QUERY_STRING} GLOBALS(=|[|%[0-9A-Z]{0,2}) [OR]
# Block out any script trying to modify a _REQUEST variable via URL.
RewriteCond %{QUERY_STRING} _REQUEST(=|[|%[0-9A-Z]{0,2})
# Return 403 Forbidden header and show the content of the root homepage
RewriteRule .* index.php [F]
#
## End – Rewrite rules to block out some common exploits.

## Begin – Custom redirects
#
# If you need to redirect some pages, or set a canonical non-www to
# www redirect (or vice versa), place that code here. Ensure those
# redirects use the correct RewriteRule syntax and the [R=301,L] flags.
#
## End – Custom redirects

##
# Uncomment following line if your webserver’s URL
# is not directly related to physical file paths.
# Update Your Joomla! Directory (just / for root).
##

# RewriteBase /index.php

## Begin – Joomla! core SEF Section.
#
RewriteRule .* – [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
#
# If the requested path and file is not /index.php and the request
# has not already been internally rewritten to the index.php script
RewriteCond %{REQUEST_URI} !^/index.php
# and the request is for something within the component folder,
# or for the site root, or for an extensionless URL, or the
# requested URL ends with one of the listed extensions
RewriteCond %{REQUEST_URI} /component/|(/[^.]*|.(php|html?|feed|pdf|vcf|raw))$ [NC]
# and the requested path and file doesn’t directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn’t directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d
# internally rewrite the request to the index.php script
RewriteRule .* index.php [L]
#
## End – Joomla! core SEF Section.

Por cierto, les dejo un vídeo para que vean algo de lo que he hecho y algo de hasta dónde he podido llegar. Es un vídeo que he encontrado después de horas buscando por google: http://www.siteground.com/tutorials/joomla-video/migration-final-steps.htm
Saludos,