Get Invalid Token at frontend login

On a site I've build my customer reports that a lot of users now get "Invalid token" when they browse the site.

I can get the same error when trying.

1. Login at the site, on frontpage.
2. Navigate to the shop
3. When in shop it looks like I'm not logged in.
4. Products in basket isn't showed.
5. Try to login again and I get the error "Invalid token"
6. Refresh the browser and everything is OK.


It is hard for them to explain this to their customers.

I have cleared the Cache in Joomla.
Session is handled in Database
No Cache plugins are active.

Problem started to happen yesterday, nothing is changed in setup since start a month ago.
Joomla 2.5.7 Hikashop 2.0

Site is www.meradog.se


Thanks


Jan

I asked my customer to check with the webhost they use and it appears that they had implemented Varnish on the server.

This line in the .htaccess file should solve the problem:
Header set Cache-Control "no-cache"

I am waiting to get this fix confirmed but I guess it can only be this since everything has worked perfectly up until yesterday when the host changed the server.


Jan

Do you know anything about this solution for Varnish:

massivescale.net/varnish-joomla.html

Jan