Online backup fails regularly

More times than not the online backup fails and I get the following information:-

1 Information 20/03/2014 04:00:01 Stage Description
2 Information 20/03/2014 04:00:02 Operation DARREN-PC started by schedule.
3 Information 20/03/2014 04:00:02 Analyzing partition '0-0'...
4 Information 20/03/2014 04:00:03 Analyzing partition '2-1'...
5 Information 20/03/2014 04:00:03 Analyzing partition 'C:'...
6 Information 20/03/2014 04:00:03 Analyzing partition '0-0'...
7 Information 20/03/2014 04:00:03 Analyzing partition 'H:'...
8 Information 20/03/2014 04:00:03 Analyzing partition '0-0'...
9 Information 20/03/2014 04:00:04 Analyzing partition 'G:'...
10 Information 20/03/2014 04:00:04 Analyzing partition 'E:'...
11 Information 20/03/2014 04:00:04 Analyzing partition 'F:'...
12 Information 20/03/2014 04:00:04 Stage Description
13 Information 20/03/2014 04:00:04 Priority changed to Low.
14 Information 20/03/2014 04:00:06 Trying to set shared lock to the file stream.
15 Information 20/03/2014 04:00:06 Shared lock is not supported by the file stream.
16 Information 20/03/2014 04:00:21 Locking partition 0-0...
17 Information 20/03/2014 04:11:06 Resending an upload request: attempt number 0.
18 Information 20/03/2014 04:20:37 Resending an upload request: attempt number 1.
19 Information 20/03/2014 04:29:51 Resending an upload request: attempt number 2.
20 Information 20/03/2014 04:35:18 Resending an upload request: attempt number 3.
21 Information 20/03/2014 04:41:01 Resending an upload request: attempt number 4.
22 Information 20/03/2014 04:46:56 Resending an upload request: attempt number 5.
23 Information 20/03/2014 04:52:35 Resending an upload request: attempt number 6.
24 Information 20/03/2014 04:59:44 Resending an upload request: attempt number 7.
25 Information 20/03/2014 05:06:50 Resending an upload request: attempt number 8.
26 Information 20/03/2014 05:14:18 Resending an upload request: attempt number 9.
27 Warning 20/03/2014 05:19:26 Canceled.
28 Warning 20/03/2014 05:19:35 Canceled.
29 Information 20/03/2014 05:19:36 Trying to unlock the file stream.
30 Information 20/03/2014 05:19:36 Unlocking is not supported by the file stream.
31 Warning 20/03/2014 05:19:36 Operation has been stopped.
32 Acronis True Image Home 20/03/2014 05:24:02 Operation has completed with errors.

Does anyone know why this happens?