Domain module not working.

One of my colleagues had issues with the domain-module while setting it up.

It was impossible to get trough the checklist of the module-configuration, while he actually followed the installation-instructions.

After some research I found that the error was related to a small typo in the settings.php .

Once I changed the settings.php cookie line to the following, it all worked:
$cookie_domain = '.example.com';

Note the preceding ‘.’ to the domain name, this is very important to get the session-handling working correctly on all subdomains.