Installing the KB2919355 update (April 2014 rollup) on Hyper-V 2012R2 introduces two separate issues:



First issue impacts backup of VMs with Windows OS versions supporting Auto Recovery functionality (Windows 2008R2 and later only) from updated Hyper-V 2012 R2 hosts. Backup of such VMs fails with the following error message:



Processing VMNAME Error: Client error: The system cannot find the file specified.

Failed to open file [\\?\Volume … AutoRecovery.avhdx] in read only mode.



Second issue impacts the entire VM restore of VMs with Windows OS version not supporting Auto Recovery functionality (Windows 2008 and earlier only), if the backup was done from updated Hyper-V 2012 R2 host. Granular recovery options work fine, but the entire VM restore fails with the following error if the backup was done from the updated Hyper-V 2012R2 host:



Writer 'Microsoft Hyper-V VSS Writer' is failed at 'VSS_WS_FAILED_AT_POST_RESTORE'



