Thread:Project:Support desk/Cannot create new users

I have just installed the latest version from Github

MediaWiki 1.25alpha (a5b6157) 14:40, 10 October 2014 PHP	5.5.9-1ubuntu4.4 (apache2handler) MySQL	5.5.38-0ubuntu0.14.04.1

When I try to create users, I am getting the following messages...

Account creation error IT Wiki uses cookies to log in users. You have cookies disabled. Please enable them and try again.

Account creation error There seems to be a problem with your login session; this action has been cancelled as a precaution against session hijacking. Go back to the previous page, reload that page and then try again.

Research has suggested a problem with permissions on the session folder, but I have checked that it is writeable, and I can see sessions in the folder.

On the same linux box, I have a second wiki installed 6 months ago. After installing I was able to create users. I have kept this up to date from Github, and I have discovered that this is now broken. I cannot create new users.

I am sure I have not adjusted any Apache/PHP settings in the interim, so I am suspecting something in the Wikimedia software.

Please can anyone suggest further debugging steps I can take ̴̴