any idea why the script fails
Well, the error seems to indicate that you, “Cannot specify user image overrides for a disk already defined in the specified image reference.” As I am not an ARM expert I’m not sure I can unwind that statement fully for you, if that’s what you’re asking. But it would seem that you’re specifying an image override for a disk that’s already defined in the image reference :).
Your PowerShell syntax is correct; the error is that Azure doesn’t like what you’re telling it to do.
This may be relevant: https://github.com/Azure/azure-xplat-cli/issues/2087
Any idea on how to fix this ?
I’m stuck with the same error… in Azure RM 6.3.0
(I’d like to mount a user-provided System Disk, a generalized VHD, by first converting the VHD to a Managed Disk)