Time Machine couldn’t complete the backup (first Backup)

Hi:

I have an ne iMac and a new LaCie 3TB hard drive running Sierra 10.12.1. The Time machine backup starts fine and then at the same point I get an error message "Time Machine couldn’t complete the backup" it indicates that if the problem persist to run disk utility on my backup disk. I have done that and everything comes back OK, I have also erase the external hard drive just in case, which by the way is formatted Mac OS Extended (Journaled) and Guid Partition Map.

I have performed a fsck -fy on the startup hard drive and everything comes out clean. Needless to say I need help!!!

Thank you for taking the time to help me!