At Login: ERROR: Cookies are blocked or not supported…

Hello all,

I have a login problem, similar to one reported by users of version wordpress 3.7. (Report here on WP Forum)

When I try to login to my blog through the ./wp-login.php I get the following error message, while I changed nothing since last time it was working (may be auto update of WP?):

Error message:
ERROR: Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.

My configuration:

Hosting: OVH

Blog: http://voyage-sur-le-fil.fr

WordPress version: 3.9.1

Theme: Set Sail (Slightly modified for French language and display behavior)

Plugin lists:
add-from-server
addsense-plugin
akismet
all-in-one-favicon
all-in-one-seo-pack
cforms
clicktale
commentluv
db-cache-reloaded-fix
exclude-pages
fb-status-updater
feedburner_feedsmith_plugin_2.3
geo-mashup
getsocial
google-analyticator
google-author-information-in-search-results-wordpress-plugin
google-image-sitemap
google-sitemap-generator
instant-adsense
like
mailchimp-for-wp
optinpop
osm
powerpress
simple-facebook-plugin
sitemap-generator
subscribe-to-comments
tablepress
tac
tweetmeme
wordpress-popular-posts
wordtwit
wp-db-backup
wp-geo
wp-super-cache
xml-google-maps
xml-sitemaps-for-videos

FTP connexion: works.

WordPress app for iOS works also

OS / Browser used to see problem:
iOS + Safari
iOS + Google Chrome
OSX Lyon + Safari
Windows 7 + Mozilla

Here is what I tried, with no success, after reading post of users with similar problem on previous WP version 3.7

Clearing username and password:
Action: I clear username field and password field of login form and enter it by hand.
Result: Not successful. The cookies error message remains the same.

Clearing cookies:
Action: I clear cookies in iOS /Safari settings
Result: Not successful. The cookies error message remains the same.

Changing of computer and internet browser:
Action: I tried on two computers I never touched before. OSX Lyon + Safari, Windows 7 + Mozilla
Result: Not successful. The error message remains the same.

Deactivating theme:
Action: via FTP, Rename folder www/wp-content/themes/set_sail adding suffix _OLD
Result: Not successful. The error message remains the same.

Deactivating plugins in one shot:
Action: via FTP, Rename folder www/wp-content/plugins adding suffix _OLD
Note: I don’t have mu-plugin folder
Result: Not successful. Following error message appears instead of login form:

Warning: require_once(/home/voyagesu/www/wp-content/plugins/db-cache-reloaded-fix/db-module.php) [function.require-once]: failed to open stream: No such file or directory in /home/voyagesu/www/wp-content/db.php on line 94

Fatal error: require_once() [function.require]: Failed opening required ‘/home/voyagesu/www/wp-content/plugins/db-cache-reloaded-fix/db-module.php’ (include_path=’.:/usr/local/lib/php’) in /home/voyagesu/www/wp-content/db.php on line 94

Deactivating all single plugins:
Action: via FTP, Rename each single folders in folder www/wp-content/plugins by adding suffix _OLD
Result: Not successful. Following error message appears instead of login form:
Warning: require_once(/home/voyagesu/www/wp-content/plugins/db-cache-reloaded-fix/db-module.php) [function.require-once]: failed to open stream: No such file or directory in /home/voyagesu/www/wp-content/db.php on line 94

Fatal error: require_once() [function.require]: Failed opening required ‘/home/voyagesu/www/wp-content/plugins/db-cache-reloaded-fix/db-module.php’ (include_path=’.:/usr/local/lib/php’) in /home/voyagesu/www/wp-content/db.php on line 94

Deactivating all single plugins BUT db-cache-reloaded-fix as it create an error instead of login form:
Action: via FTP, Rename each single folders in folder www/wp-content/plugins by adding suffix _OLD but db-cache-reloaded-fix folder
Result: Not successful. The cookies error message remains the same.

Commenting lines in wp-login.php
Action: Via FTP, I commented line issuing the cookies login error.
Result: Not successful. A new error message appears telling my username/password is wrong… wich is not true !

So, I have no idea what to try next !

Your help will be highly welcome, as I feel outside of my own house now