plc blind tripping

hi all,
we have been facing blind plc tripping of control logix 5555. all of sudden all cards starts blinking and communication is lost. we could not be able to find what major or minor fault came in. Only solution is to cycle power as stated in LOGIX help. after doing the same "connected to controller" dialog box appears and major error displayed as "power up fault" unrecoverable fault error code 60" which is probably due to power cycling from MCB. the original reason for plc failure is still unknown.after same failure plc ran successfully for 6-7 months and failure occured on yesterday. Our process manager said i never seen PLC failure in my previous company. is there any problem with ground loops or earthing problem. earth resistance is 5.5 Ohm between neutral and earth.

There are at least two possibilities Ican think of from recent memory.

See ab.com for Technical Note ID 41204...too large to attach

And another one regarding firmware issues which could cause the Logix processor to shutdown after a certain number of days.

I will try to find the links


Edit: Attached file for the other lockup issue...

Thanks for reply.
that is of great help.
one other thing is that we have ground loop problem , DMM is showing 24vdc between transmitter +ve lead and instrument housing or any metal object of plant. few transmitter also showing display after removing -ve 24vdc wire. is it affect PLC hangout. will you please give me some advise with correct grounding/earthing. here in india we are not using shields and in one GTG panel which came frm US, they have used shields in whole wiring.