Access to raw partition on Windows8

[neo42]

I am trying to create a vmdk file to access my Ubuntu linux partition on the physical ssd of my notebook from a virtual machine. But when I try to access the physical drive, even with

VBoxManage internalcommands listpartitions -rawdisk \\.\PhysicalDrive0

I get

VBoxManage.exe: error: Cannot open the raw disk: VERR_ACCESS_DENIED

Any ideas how I can find out what prevents me from accessing my ssd?

[mpack]

Enabling raw access to Win7 and later disks.
viewtopic.php?f=6&t=38914#p175089