360 Premium back up failure to new My Book

After I back up I can see the back up file on My Book but at 99% of the back up - it says there was an error and gives me this message

 

Unauthorised access blocked (access Process data)

 

Actor: C:\WINDOWS\SYSTEM32\CONHOST.EXE

Actor PID: 7844

Target: C:\Programme Files (x86)\Norton 360\Engine64\21.6.0.32\buvss.exe

Target PID: 6472

Action: Access Process Data

Reaction: Unauthorised access blocked.

I have a Sony Vaio Laptop and I set Norton to back up to My Book on the correct drive.

 

i don't have a clue what all the above means but can anybody identify what or if I am doing something wrong please?

Thanks

BoSS  ;)