ML6000 Robotics communication failure

I m facing the above issue with Ml6000 library with 1 12U expansion. 
we have replaced the robotics, spool cable, module to module terminator cable, PDU of the main expansion. 
still we are getting same error on the library. 
we have also upgraded the firmware of the drives and library. Still issue is same. 

library initialises without any error. It runs for almost 20min to 25mins after which Leds on robotics are gone. 
after reboot led on robotics are not turned on. After power drain leds are back and library initialise again without any error. 

can anyone suggest if LCB is to be replaced? 
and if it is to be replaced how to replace it without hampering the license of the library.

thank you.