APIC failing to form Cluster

[ataranen]

I have 3 APIC controllers running version 1.2(3c). 
After doing the initial setup and discovering fabric nodes, the APIC do not form a cluster. The 1st controller is "available" while the other 2 get listed as "Unauthorized Controllers" as shown in the attached image.
I reinstalled the OS, and made certain the initial configuration is correct, still nothing. What could be the issue ?  

[ataranen · Accepted solution]

Found the cause. 2 apic's had a clock out of sync. After changing clock on the server using F2 option, the cluster has formed. 

[arpitagu]

How I can change the clock of the controller which is showing under unauthorized.

Unauthorized controller is not giving any output of "show clock"