Cisco Wireless APs fail to associate to the controller.

We had an issue with a 1200 series lightweight AP not associating with a 2100 series wireless controller.  During investigation and I found a certificate error associated to the LWAP join request.  Because I had the flexibility to do so, I thought "let's reboot the controller and see what happens".  After reboot none of the APs were associating and all were having the same error.  Not a good result.


I discovered this article
https://supportforums.cisco.com/document/12453081/lightweight-ap-fail-create-capwaplwapp-connection-due-certificate-expiration

In addition, without an upgrade and certificate check disable, a quick fix to get the APs associated is to change the date.  Simply disable NTP on the WLC and set the date back a few years.  The APs associated right up and everything started working.