Mystery Fault

My PLC occasionally faults out and give me this fault message. Any ideas guys?

You used a resolution too low for the images that I can hardly read the error message (Value out of range) or the equations in the logic. I only can suppose that you're indexing an array and the index is going out the valid range.

nhatsen is correct. The fault information points to rung 2. The forst contact is rung 2 uses an index to determine the bit. I suspect that index is calculating to a value greater than the available bits.

Keith