This error message appears while you monitor the activity on the controller:
Error for AIR-LAP1231G-E-K9
Day Month Date 00:00:00 Year: <_128> [CRITICAL] sshpmPkiApi.c 1530: Invalid AP certificate - unknown issuer
Day Month Date 00:00:00 Year: <_130> [ERROR] spam_lrad.c 4880: LWAPP Join-Request does not include valid certificate in CERTIFICATE_PAYLOAD from AP 00:00:00:00:00:00
The Wireless LAN Controller (WLC) 4136 does not support the Cisco IOS Software Release 126.96.36.199 Lightweight Access Point Protocol (LWAPP) APs. It supports only 4400 and 2100 series controllers, and Wireless Services Module (WiSM) supports Cisco IOS LWAPP APs, so there is no workaround for WLC4136. Therefore, the access point (AP) 1231 does not join to a 4136 or 4100 series controller at any code version.