Automatic Backup Failed, No Reason Given

I have setup 7 backup sets. When I use the "Run backup now" option, they work fine. But when the backup starts when the machine is idle, I get a message in the security history, saying that the backup as failed, with no error message.

The backup is done to a 4TB Seagate external hard drive, with 1.7 TB of free space.

The external drive is setup so that it never goes in power saving mode.

Backed up files are documents, pictures, movies which takes about 500MB.

 

Any idea why this happens?

Thanks.

Its been a few days and my automatic backups are working fine, ~every 24 hours at idle; I'll assume deleting the backup archive from Explorer and refreshing the list in N360 (to clear it) was the fix.

No. It is set up to never go to sleep.

I have setup 7 backup sets. When I use the "Run backup now" option, they work fine. But when the backup starts when the machine is idle, I get a message in the security history, saying that the backup as failed, with no error message.

The backup is done to a 4TB Seagate external hard drive, with 1.7 TB of free space.

The external drive is setup so that it never goes in power saving mode.

Backed up files are documents, pictures, movies which takes about 500MB.

 

Any idea why this happens?

Thanks.

New info: Today I got 3 failures, 4 success and one partial success.