UPDATE 1

Veeam have confirmed that this issue is related to Veeam Backup & Replication.  They’re working on a fix for the general availability (GA) release of the Windows Server 2012 R2 Update.  Follow this link on the Veeam forum for updates.

UPDATE 2

Veeam have released the hotfix and it’s available through support.

UPDATE 3

Veeam have identified a second issue.  Restoring Windows 2008 and earlier backups made on an updated Hyper-V 2012 R2 host fails.  The Veeam KB article is available here 

Having installed the Windows Server 2012 R2 Update, my Veeam Hyper-V backups failed with errors as shown below.

03/04/2014 20:58:28 :: Processing ‘SERVERNAME’ Error: Client error: The system cannot find the file specified.

Failed to open file [\\?\Volume{36db85be-bb6a-11e3-80ce-000af72f0333}\SERVERNAMEWINDOWS SERVER 2012 R2 STANDARD_DISK_1_117A5A0B-5976-4766-B256-3707A2D8CFA7-AutoRecovery.avhdx] in readonly mode.

The engineer at Veeam (Anatoly) was excellent and was able to prove that the error wasn’t related to Veeam by running Windows backup commands using PowerShell.  Following the uninstall of KB 2919355, the only one of the six hot fixes comprising the Windows Server 2012 R2 Update listed in Add Remove Programs, I was able to run backups as before.  If you’re thinking of installing this update ensure you test it well.

For reference the configuration is:

• 4x Hyper-V 2012 R2 hosts
• Dell EqualLogic SAN 6.0.7
• HIT Kit 4.7 EPA
• Veeam Backup & Replication 7.0.0.839