With the settings I have, it is apparently shutting down due to a raid error. It shouldn't shut down for any other reason.
It has a "sleep" mode and a "Synchronize with UPS" setting that are both disabled.
The only setting I have enabled which would cause it to shut down is "Automatic Shutdown" in the "RAID Array Error Detection Response" section of the RAID Configuation settings page.
This just started happening in the past week or so. Since it appears to be shutting down due to RAID errors, I'm obviously concerned and just trying to figure out a next step. It seems like there should be a log file somewhere that would give me some kind of clue as to what the problem with the RAID is, or what the errors are/were, but I can't find any log anywhere.
Every time it happens I just power it back on, it does a disk check that takes a few hours, then it resumes normal operation at which point it will shut down again in anywhere from 1 to 24 hours.