After the upgrade to Windows 10 1511 I cleaned up the old Windows installation but I noticed that C:\Windows.old was still present.
I found these files:
I was not able to delete these files and the reason is that the files I’m trying to delete are hardlinks to corresponding files in C:\Program files…. and they are loaded drivers (STMicroelectronics 3-Axis Digital Accelerometer) and are therefore open in the OS.
The solution is to stop the driver. To do that:
Open Device Manager (Control Panel)
Expand System Devices
Find STMicroelectronics 3-Axis Digital Accelerometer and double-click
Select the Driver tab
Now you can remove those hardlink files in C:\windows.old
Go back and click Enable on the STMicroelectronics 3-Axis Digital Accelerometer Drivers tab.