When imaging a new Generation 1 Hyper-V Server 2008 R2 machine, the task sequence would fail. The smsts.log showed “Failed to make volume C:\ bootable. Please ensure that you have set an active partition on the boot disk before installing the operating system. Error: 80004005”
I tried using CMD support (F8) in WinPE and using diskpart to make the partition active/format the disk and run the Task Sequence again, but the same issue.
This fix was an easy one. I just deleted the virtual hard disk (vhdx) and created an other one, cleared the PXE flag and it re-imaged successfully. Not sure what was wrong with the original VHDX file. It still appeared as a C:\ with files in there.