ReadyNAS 3138 - Regularly rebooting itself

Hi all:

I'm hoping someone can help me with an issue I'm having with my RN3138.  It's been installed in a nicely cooled IT room for about 8 months with no issues.  It's completely isolated from the internet and 99.9% of the traffic on the NAS is from Acronis Backups of about 15-16 computers.

Now, in the past 48 hours, it has started rebooting itself every 5-8 hours.  

I've downloaded the log files - which I've discovered are many - and picked through each and every one.  A lot of these, as you might be aware, are just configuration summaries.  But for each of the files with timestamps, I see a line that says "-- Reboot --". 

Unfortunately the "Reboot" line is the only one that's not timestamped.  

I've picked through every log file, and looked at the preceeding log entries.  Most of them are hours or even days before the reboot.  They seem completely irrelevant to me - although I'm not an expert on the ReadyNAS OS.

As a shot in the dark, I upgraded from OS 6.6.0 to the latest (6.7.5).  But then I saw a reboot again within a couple of hours.  I picked through all the log files again to see if there was anything else - nothing.

Anyone have any suggestions? I don't see a way to attach, but would be happy to upload log files if there's a place for that.

Thanks.