Frustrating problem with scheduled scans

Norton 360 Premier, Win 8.1 64bit.  Automatic Win updates.  Norton is set to also automatically check for new versions.

 

I have a full scan scheduled for 3am daily.  

 

The full scan works properly for 2 days (3 if I'm lucky) then fails to run.  I reboot.  Full scan works properly for 2 day then fails.  Reboot.  Works for 2 days.  

 

I have the same problem with Quick Scans.

 

I have a similar problem when I try to run a custom scan after 2 days.  I get an error 3808, 404  (that's from memory, it could be slightly different).  Reboot and custom scans work fine.

 

Live Updates also stop working after about 3 days.  Reboot and they start working.

 

I've tried changing the scheduled time but that makes no difference.

 

This is becoming a real nuisance.  I don't have similar problems with any other programs, it's just N360.  Any suggestions?