Wifi authentication issue with Marshmallow?

[AC Question]

I've just completed the update to Marshmallow on my 2014 Moto X. Now I get an "authentication problem" when trying to connect to my company's guest wifi. I've tried the basics: wifi on/off, forget the network, toggle 2.4 GHz / 5 GHz / Auto.

Still no connection. Any suggestions?

 

[B. Diddy]

Welcome to Android Central! Are you able to reboot the router at work, or can you get somebody to do it?

 

[Leonardo Angelo Lopes]

I'm having the same issue on my Moto X Style.
A friend of mine rebooted the router, but it won't connect anyway.

When I type the password, it says "Saved"
And then "authenticating". Then "authentication problem". And "saved" again.

Now I can't use WiFi at work.