“Error applying Hard Drive changes” on Generation 2 VMs

A Microsoft employee recently contacted us with this issue:

“When I try and attach a virtual hard disk to a generation 2 virtual machine – I get an error message that says ‘Error applying Hard Drive changes’”

It took a bit of conversation – but eventually we figured out what was happening.  Here is the error message in action:


What is happening here? The answer is that we only support .VHDX files with generation 2 virtual machines.  You cannot attach a .VHD file to a generation 2 virtual machine – and if you try to do so you will get the error message above.

If you have a .VHD file that you want to connect to a generation 2 virtual machine, you should convert it to a .VHDX first.