ATI 2015 will not start Back up under Windows 10

I have been running Win 10 for about 2 months, with Acronis True Image 2015 (latest build) operating reliably on a daily backup schedule until the 22 September. It then stopped running back ups. Upon much reading and investigation I have found that the 1TB Seagate USB drive I am using for Acronis Backups, is apparently failing to be accessed because of the following returned error -
\Device\HarddiskVolume4\Windows\System32\SVChost.exe. This error is returned when (in desperation ) I attempt to "Safely Disconnect" the drive. ????
The only way I have been able to progress is to "delete" this object via Windows Explorer, using the 3rd party program "Unlocker". After a reboot, the (error?) message is not generated when unplugging the USB drive. After plugging it in again, and starting True Image, a backup is again able to started.
However, after a couple of days the same problem recurs.

I would really appreciate any informed assistance you can provide.

Ian Kettlewell