I'm also experiencing this problem. I just opened my brand new J5IK and was working through the Experiment Guide, marvelling at the excellent quality of the tutorial, and everything was going as expected until issuing the
t2 update command. I see the following:
INFO Looking for your Tessel...
INFO Connected to grandalf.
ERR! Error: certificate has expired
I searched for the error via Google and it brought me here. (First post! Hi!)
t2 version produces the same error.
I've tried all the obvious things; rebooting, cycling power on Tessel2, changing USB ports (at some point
t2 list stopped reporting my Tessel.)
Has anyone tried using LTS v4.4.5, the version specified in the Experiment Guide? I installed the latest node.js which is v6.11.0.
EDIT: I changed my system date back one year (6/11/2016) and
t2 version and
t2 update appear to work as expected.
EDIT2: Rolling back the system date seems to have allowed firmware update v0.0.16 to succeed but necessitated going through a lot of the setup steps again (like naming my network and setting up wifi.) Unfortunately setting the system back to the correct date causes
t2 version to display "certificate has expired" so the problem still exists. I'm going to try to proceed with the Experiment Guide. I know software is complicated but i'm pretty bummed that this beginner kit is exhibiting these problems.