After installing November roll-up update http://support.microsoft.com/kb/3000853 on 2012 Hyper-V hosts, VSS-enabled backups may be failing in any backup solution.
In Veeam you will get "Unable to allocate processing resources. Errors: Failed to create snapshot for vm..." The error message in logs is as follows:
<01> Error Failed to analyze snapshot availability for task '1c6d5578-8e5f-4fea-89b7-33afee0dfaf0' (System.Exception) <01> Error at Veeam.Backup.ResourceScheduler.CHvSnapResDispatcher.CanAcquireResource(CResDispatchIterationContext dispatchContext, CResourceTask task, IResourceRequest resourceRequest, IResourceResponse acquiredResources) <01> Error at Veeam.Backup.ResourceScheduler.CResourceTaskScheduler.IsAllResourcesAvaliable(CResDispatchIterationContext dispatchContext, CResourceTask task) <01> Error at Veeam.Backup.ResourceScheduler.CResourceTaskScheduler.DispatchPendingTask(CResDispatchIterationContext dispContext, CResourceTask task) <01> Error Failed to create snapshot for vm 5864ae48-bc3c-4cd9-9503-f637da801ccb (System.Exception)
Replication job may yield the following error:
<13> Error Value cannot be null. <13> Error Parameter name: node at Veeam.Backup.Common.CXmlHelper2.TryToGetAttrInternal(XmlNode node, String attrName, String& foundValue) <13> Error at Veeam.Backup.Common.CXmlHelper2.GetAttrAsString(XmlNode node, String attrName)
The issue occurs because the Volume Shadow Copy Service (VSS) encounters a deadlock during the Thaw event if the Security Account Manager (SAM) has pending writes for the registry.
Microsoft is aware of the issue and is working to resolve this. Uninstalling KB3000853 update should resolve the issue (reboot required).
The hotfix has been issued as well http://support.microsoft.com/kb/2996928/
Please be aware that we’re making changes which will restrict access to product updates for users without an active contract.