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Cisco 5520 and 8540 Wireless Controller Troubleshooting Guide
 
  Troubleshooting
• Check if Serial-over-LAN is disabled in CIMC
• Get the status of this from the Telnet/SSH to controller using
show imm chassis sol-info
Note When Serial-Over-LAN is enabled all external consoles will be disabled.
APs not joining with and displays certificate Error / Certificates not found
Solution
• Check if the certificates are installed and not certificate errors were seen during bootup
Show certificate all
The above command shows the certificates present/installed and status
• Check if the FlexFlash is present in the SDcard panel in UCS
• Check if the Flexflash is connected to HOST
If we remove the SDcard while WLC is powered on, it will get disconnected and cannot be accessed in 
subsequent boots as well.