Processor Dropping Program

Yes, heat is a real problem.

This Wiki article about it is pretty good.

I just went through this. A few minutes with a can of compressed air helped a whole bunch. I also discovered that one of the fans had been turned off in the setup menu, where these are monitored and controlled.

Sounds as though someone got sloppy on the environmental design considerations.

CompactLogix L3x series controllers are rated for 60C (140F) operating temperature, probably the highest in the industry for something of that power. If you have it in a sealed enclosure with no vents, no air conditioning, or exposed to the sun or other source of ambient/radiant heat, even that high of a spec will be easily exceeded especially if the power supply and anything else is inside the same box. You need to either ventilate it (safely) or add an air conditioner if you cannot. If it is in the sun, put a sun shield over it. If it is next to something hot, like an oven, move it away.