S7-1200 crashing on Cycle Time...

[lostcontrol]

Hi, I am getting these errors, causing the CPU to stop on us. For the first error, DM18 is not being accessed, so not sure why that is being displayed. Is it possible that a previous DB is having a bounds errors? The machine has a Input interrupts that are consistent intervals depending on the machine speed. Typical cycle time is 10ms, with a max of 13ms been observed. I have tried extending the max cycle time to 500ms from 150ms & it still happened. My suspicion is that it is not interrupt related, but something else, perhaps a bounds error. Any suggestions for narrowing this down? It is intermittent, but happening more frequently now.