I'm not sure (since you're running PHP on IIS/Windows), but I think the PHP settings you have for
session.save_handler files files
session.save_path no value no value
aren't quite right. The save_handler says files, but no path is specified.
For my PHP on Apache/Linux, those values look like
session.save_handler files files
session.save_path /var/lib/php/session /var/lib/php/session
(note the default session.save_path points to a PHP writable directory