I've been getting this error today when I tried working on my Wiki. I just installed MediaWiki about a week ago and have been edited every single day with no issues at all... until today.
How do I assure that cookies are enabled? I did some basic research online, and I was told to edit the session.save_path... I don't have that. I have no idea where to find my php directory that has these files. I've looked everywhere and it's quite frustrating.