Backup job fails with status code 156

[meninblack]

26/05/2014 18:07:11 - end Create Snapshot; elapsed time: 00:07:06
26/05/2014 18:07:11 - begin Flash Backup Windows, End Notify Script
26/05/2014 18:07:11 - Info RUNCMD(pid=6892) started
26/05/2014 18:07:12 - Info RUNCMD(pid=6892) exiting with status: 0
Status 0
26/05/2014 18:07:12 - end Flash Backup Windows, End Notify Script; elapsed time: 00:00:01
Status 156
26/05/2014 18:07:12 - end Flash Backup Windows, Create Snapshot; elapsed time: 00:07:08
snapshot error encountered(156)

Any ideas?
Thanks