I wouldn't get hung up on the second part of the error.
The problem is that sessions don't work. One possible reason is that the browser you are using doesn't support cookies but, to be honest, I find that unlikely (unless you are running some cookie blocking extension).
Start with the basics, enable debugging (by copying section 7 from config-dist.php to your config.php), reproduce the error and check your web server's error log for anything diagnostic.