Problem: GandiBlog does not allow metadata editing nor root directory file uploading

Traduction Française?
Error:

We couldn't find the verification meta tag

We've detected that your verification file returns a status of 404 (Not found) in the header.

Verification failed. Your verification TXT record record was not found.

Solution: Use Google's DNS TXT record method OR forward the domain you own directly to an HTML file that has the verification tag.

DNS Record Method

Français: gandi.net -> Domaines -> Gérer les zones -> Ajouter un enregistrement -> Type: TXT, TTL: 1 heures, Nom: blanc!, Valeur: google-site-verification: Abc123 -> Valider -> Valider les changements

Step 1: Log into gandi.net and go to your domain's control panel; in the DNS section, click Manage your zone file; the page will show a list of records, click the Add an entry button below the list.

Step 2: Add a Record: for Type choose TXT, for TTL choose 1 hour (less would update the DNS faster), for Name leave it blank!, for Value copy and paste the record Google gave you (google-site-verification: Abc123), then click submit; when you are back in the records list, you must click Submit changes to confirm the change.

Step 3: Wait about an hour then go to the Google Webmaster page to do the verification by DNS method. If you entered everything correctly and waited long enough, the verification should pass.

Example of the resulting line in the Zone File: @ 3600 IN TXT google-site-verification: TI7mWwUKAMHSSLhoN7w6b4oEcyGnaSbrylS7e7iv

Alternate Redirection Method

If the DNS method did not or cannot work, try this method instead:
Step 1:  Right click and save this file verify.html, open it with a text editor and then paste the meta tag Google gave you, for example: 
<html>
<head>
<!-- Insert Google's verification meta tag below this line -->
<meta name="verify-v1" content="EXAMPLEmiEv5ubIU2L98oAMIajLAtI2t/Oe9Riacri5xo=" />
<!-- Insert Google's verification meta tag above this line -->
</head>
</html>
Step 2:  Go to your blog's Dashboard -> Media manager and upload your verify.html
Step 3:  Go to gandi.net -> Manage tab -> Technical Settings section -> Web section -> Gandi Blog: Active Update and rename your Gandi blog's address from blog.yourdomain.com to tempblog.yourdomain.com. Then go to Forwarding: active Update and add or change the domain/subdomain you want to verify so that they point to your tempblog's verify.html
Example Result: 
Blog of yourdomain.com
The blog's address       Status
tempblog.yourdomain.com  Active

yourdomain.com - Web forwarding
Subdomain            Type               Destination Address
blog.yourdomain.com  Direct (permanent) tempblog.yourdomain.com/public/verify.html
www.yourdomain.com   Direct (permanent) tempblog.yourdomain.com/public/verify.html
yourdomain.com       Direct (permanent) tempblog.yourdomain.com/public/verify.html
Step 4:  Wait for Gandi to update the addresses; it may take 1-3 hours for the DNS to change. Each Google verification tag is unique to that domain, so after you finish verifying blog.yourdomain.com, add yourdomain.com or www.yourdomain.com to Google Webmaster Dashboard and get another tag. Copy this new tag over the old tag in your verify.html, reupload it, and ask Google to verify that domain.

Conclusion:  You only need to verify once, so reforward your blog and domains back to its former addresses after it is all done. You can now submit a sitemap.txt without Google's "current-directory restriction".

Resources: Google Webmaster Help
Keywords: Add a DNS record, Domain Name System, google-site-verification, non validé, validation, Nous avons constaté que l'en-tête de votre fichier de vérification renvoie un code d'état 404 (Introuvable)