VSS Error with VM Snapshots

VMware 5, VDR 2.

1 VM is unable to be backed up because of error:

Failed to create snapshot for DC, error -3960 ( cannot quiesce virtual machine)

This was the only machine being backed up at the time and the host is otherwise under no load, so I dont think this is an I/O problem. Destination is a NAS drive (NFS) on a 1GB link LAN,

Had a search about, and I think it is to do with VSS on the Guest OS.

As per this article: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1018194

Eventvwr on the OS has a single error 11: The driver detected a controller error on \Device\Harddisk2\DR2.

And cmd > vssadmin list writers gives lots of errors:

C:\Users\administrator.EVO>vssadmin list writers
vssadmin 1.1 - Volume Shadow Copy Service administrative command-line tool
(C) Copyright 2001-2005 Microsoft Corp.

Waiting for responses.
These may be delayed if a shadow copy is being prepared.

Writer name: 'Task Scheduler Writer'
   Writer Id: {d61d61c8-d73a-4eee-8cdd-f6f9786b7124}
   Writer Instance Id: {1bddd48e-5052-49db-9b07-b96f96727e6b}
   State: [1] Stable
   Last error: No error

Writer name: 'VSS Metadata Store Writer'
   Writer Id: {75dfb225-e2e4-4d39-9ac9-ffaff65ddf06}
   Writer Instance Id: {088e7a7d-09a8-4cc6-a609-ad90e75ddc93}
   State: [1] Stable
   Last error: No error

Writer name: 'Performance Counters Writer'
   Writer Id: {0bada1de-01a9-4625-8278-69e735f39dd2}
   Writer Instance Id: {f0086dda-9efc-47c5-8eb6-a944c3d09381}
   State: [1] Stable
   Last error: No error

Writer name: 'System Writer'
   Writer Id: {e8132975-6f93-4464-a53e-1050253ae220}
   Writer Instance Id: {d6e54a9f-297b-4e7d-9a63-39f445907f33}
   State: [10] Failed
   Last error: Timed out

Writer name: 'FRS Writer'
   Writer Id: {d76f5a28-3092-4589-ba48-2958fb88ce29}
   Writer Instance Id: {dadc4e12-412a-4613-8e55-0e935a1d43ea}
   State: [10] Failed
   Last error: Timed out

Writer name: 'ASR Writer'
   Writer Id: {be000cbe-11fe-4426-9c58-531aa6355fc4}
   Writer Instance Id: {b29b4aad-d175-4906-afb0-1da1e9fdfd7b}
   State: [1] Stable
   Last error: No error

Writer name: 'SqlServerWriter'
   Writer Id: {a65faa63-5ea8-4ebc-9dbd-a0c4db26912a}
   Writer Instance Id: {4af7caa2-af9f-4f87-9d59-8304e50016c7}
   State: [10] Failed
   Last error: Timed out

Writer name: 'NPS VSS Writer'
   Writer Id: {35e81631-13e1-48db-97fc-d5bc721bb18a}
   Writer Instance Id: {9a0cd13c-ccd5-4e2e-94cc-d5afe8d951f2}
   State: [10] Failed
   Last error: Timed out

Writer name: 'Dhcp Jet Writer'
   Writer Id: {be9ac81e-3619-421f-920f-4c6fea9e93ad}
   Writer Instance Id: {f0d61536-8d0d-4ca4-8565-c349d17f3b3b}
   State: [10] Failed
   Last error: Non-retryable error

Writer name: 'Backup Exec Deduplication Storage Writer'
   Writer Id: {55f6d76d-8617-4fc8-81e9-df0de529b555}
   Writer Instance Id: {02b3b2f7-249a-4142-996a-5a4e7be94ae2}
   State: [1] Stable
   Last error: No error

Writer name: 'WMI Writer'
   Writer Id: {a6ad56c2-b509-4e6c-bb19-49d8f43532f0}
   Writer Instance Id: {3c24d2c2-7f9a-4f33-aa4f-034ff71962b5}
   State: [10] Failed
   Last error: Timed out

Writer name: 'NTDS'
   Writer Id: {b2014c9e-8711-4c5c-a5a9-3cf384484757}
   Writer Instance Id: {49100f8b-c054-41f3-83c4-d982ddca84de}
   State: [10] Failed
   Last error: Non-retryable error

Writer name: 'COM+ REGDB Writer'
   Writer Id: {542da469-d3e1-473c-9f4f-7847f01fc64f}
   Writer Instance Id: {fad48f52-b286-467a-ac64-702b12f625b6}
   State: [1] Stable
   Last error: No error

Writer name: 'Registry Writer'
   Writer Id: {afbab4a2-367d-4d15-a586-71dbb18f8485}
   Writer Instance Id: {ed91fa86-31e5-456e-a1e0-c0e1fe9cbc8c}
   State: [1] Stable
   Last error: No error

Writer name: 'Shadow Copy Optimization Writer'
   Writer Id: {4dc3bdd4-ab48-4d07-adb0-3bee2926fd7f}
   Writer Instance Id: {dd54ed26-18e9-4451-9580-1e70873c70f3}
   State: [1] Stable
   Last error: No error

How should I proceed?