Hi Steve - I had this same problem with one of my LinkStations, it has 1.x version firmware. For about a month the LS would shut down every 5 - 7 days but left no error logs or warnings. I got the daily email saying there were no errors so I didn't worry too much about it. I did run disk checks but the LS reported no issues.
I checked settings to ensure the LS was not set to shut down after detecting an array error. It wasn't.
I have since lost access to the entire LS. So, I advise you to look carefully at your disks and to back things up away from the questionable LS if you can! Luckily I have a second LS and I split the NAS duties between the units and used part of each unit to back up the other. Maybe inefficient in terms of disk usage, but saved me in this case.
What happened to me? Two weeks ago the number 1 disk failed - reporting that the LS could not detect a partition. Disk check still reported no errors. Then, several days later it reported that a disk error was detected, the disk was removed from the array.
I attempted to replace the disk. I've done it for disk 2 ~ 8 months ago - so a known procedure, no big deal.
This time problems though - when LS came up with the new disk it errored for formatting - expected.
What was not expected - all the user id's and passwords are lost. The same ones I used to shut the bugger down are no longer recognized. Admin, guests, and all registered user ID's are unrecognized. My attempts to load new firmware say that it's all up to date, and the defaults don't work either.
Hope this isn't what happens to you, but that's my experience.
I'd appreciate any suggestions you have for me.
Good luck,
Bill Fuson