Failed to create the backup of virtual machine

hi sysadmins.

i'm no expert in ms windows systems , need fixing backup issues.

we have 2 physical machines running  windows server 2008 r2 enterprise sp1 hyper-v host 3 virtual machines each - domain controller, exchange server, file server, running  windows server 2008 r2 enterprise sp1.

the problem is, since september weekly backups fail each time, on both machines.

backup configured task scheduler job:

wbadmin start backup -backuptarget:e: -include:d:\vms -vssfull -quiet

where e backup disk (155gb free of 600gb), , d:\vms location, virtual hard disks , virtual machines stored.

backup used work several weeks. windows server backup shows 24 number of copies, latest available from 28-09-2013.

i have registered vss writer: 

[hkey_local_machine\software\microsoft\windows nt\currentversion\windowsserverbackup\application support\{66841cd4-6ded-4f4b-8f17-fd23f8ddc3de}]"application identifier"="hyper-v"

running vssadmin list writers gives me:

writer name: 'microsoft hyper-v vss writer'
writer id: {66841cd4-6ded-4f4b-8f17-fd23f8ddc3de}
writer instance id: {91a24129-d7fe-4539-98e6-ed008610873a}
state: [5] waiting completion
last error: retryable error

following errors occur in event viewer:

event id: 10107 (warning)

one or more physical disks attached virtual machine 'slx-lu-ex1'. programs use hyper-v vss writer cannot volumes attached virtual machines physical disks. avoid potential data loss, use method data on physical disks. if restore data on virtual machine, make sure check data of physical disk integrity. (virtual machine id e7b82301-709c-4002-874c-c235dfb3c71a)

event id: 10102 (error) 

failed create backup of virtual machine 'slx-lu-fs1'. (virtual machine id b1cc6fa8-824d-4e95-af06-27e3164182ea)

and event id 521

the backup operation started @ '‎2013‎-‎11‎-‎09t22:30:11.707000000z' has failed because volume shadow copy service operation create shadow copy of volumes being backed failed following error code '2155348129'. please review event details solution, , rerun backup operation once issue resolved.

also, i'm not person configured whole thing, please advice if proper way of making backups.

according event id  10107, machine  slx-lu-ex1 have connected 3 phisical drives exchange databases, logs and journaling, there disks mounted since beginning.

hi, i'm afraid couldn't more wrong :)

event id 10107 hyper-v vmms (warning) states:

one or more physical disks attached virtual machine 'xxxxxx'. programs use hyper-v vss writer cannot volumes attached virtual machines physical disks. avoid potential data loss, use method data on physical disks. if restore data on virtual machine, make sure check data of physical disk integrity

it possible backup vm machine, when contains  physical disks , i'm doing right now.

i'm managed resolve issue, backup in progress. however, direct cause of 2155348129 vss error code remains unknown after extend research has been made.

i installed updates on guests , host os, , rebooted machines.

i think got corrupted , reinitialized after reboot. before windows updates switched off vms restarted @ least once month.

Windows Server  >  Hyper-V