Issue with Mitsubishi A series PLC

Hi guys,
I am facing a recurring problem in a Mitsubishi make PLC installed at my facility.The PLC is of mitsubishi make, A series & has 8 modules in its rack.The issue is that the PLC stops functioning abruptly displaying an error "SP down".Now there are 4 special function module installed in the rack & i have checked all of them but could not find anything unusual.

The error is very abrupt & random in nature & clears automatically after some time.

I am at a loss to understand the cause of this issue....pls help

You will need the software to check the error.

But. the 'A' series is getting old now and failures are common with the CPU and backplane connections.
Have you tried taking the units out of the backplane and reseated them?

I have checked the error code using the software & it shows up as "SP DOWN" & "SP ERROR" .

Will loose installations on the rack result this error which clears itself after some time??

I have seen strange intermittent errors like this caused by moisture on the backplane PCB on A Series PLC's before. Is the backplane completely clean and dry?

The backplane is clean but I have observed that the entire panel is vibrating a little more than usual when it the machine runs.

Could this be indicative of anything??