Performed upgrade of Civi 4.4 to 4.6 alongside upgrade of Drupal from version 6 to version 7. The Drupal upgrade went fine, as did the CiviCRM upgrades (i.e. no errors were reported).
All dashboards and search functions in CiviCRM work fine, but as soon as I try and create anything (e.g. registering for an event, creating a new Individual, etc...) we get the error: "Could not find valid value for ct".
Searching forums showed this is an old error related to sessions, so checked over all the PHP.ini and Nginx settings to ensure cookies and other domain related settings were correct.
Can anyone point me in the right direction of where else to look?
** EDIT *** Additional error messages being shown after enabling debug:-
Sorry but we are not able to provide this at the moment. We can't load the requested web page. This page requires cookies to be enabled in your browser settings. Please check this setting and enable cookies (if they are not enabled). Then try again. If this error persists, contact the site adminstrator for assistance.
Site Administrators: This error may indicate that users are accessing this page using a domain or URL other than the configured Base URL. EXAMPLE: Base URL is http://example.org, but some users are accessing the page via http://www.example.org or a domain alias like http://myotherexample.org.
Error type: Could not find a valid session key.