Just encountered this problem after fully patched Windows Server 2012 Hyper-V.
- Running failover cluster with Hyper-V installed
- Created virtual machine and add virtual hard to the VM.
- Some virtual hard disk can add but some failed to virtual hard disk to the VM.
- Error message when add virtual hard disk:-
1. Found the solution, that we need to install with KB2836402 hotfix
2. Apply the hotfix
3. Reboot the Hyper-V host