Surface Pro 4 Unattended Sysprep Issue

Hi Guys,

Im attempting create an unattended sysprep windows 10 installation (1607) for the Surface Pro 4 using a USB and WinPE. I dont have the current script with me but the process is roughly the following;

Install win 10 - audit mode
Generate an unattend.xml using windows ADK and generating a catalog file
sysprep.exe /generalize /oobe

I then boot into WinPE and capture the ESP and the windows image (c:/)

Now for the problem. Upon booting into WinPE on the target Surface Pro 4 i have a script running that basically preforms the following process:

Diskpart
Select disk 0
Clean
Convert gpt
Create partition efi size=200
Assign letter=s
Format quick fs=FAT32
Create partition msr size=128
Create partition primary
Assign letter=c
Format quick fs=NTFS
Exit

In the script i then apply the images to the correct partitions using dism, and then run these commands based on this resource:
https://technet.microsoft.com/en-us/library/cc765951(v=ws.10).aspx


bcdedit /set {bootmgr} device partition=s:
bcdedit /set {memdiag} device partition=s:

bcdedit /set {default} device partition=c:
bcdedit /set {default} osdevice partition=c:

Bcdedit /set {FWbootmgr} displayorder {Bootmgr} /addfirst


I have highlighed in blue where the script has a problem. Ignore the black rectangles in the screenshots but as you can
see when the script reaches the point to create the drive letter c i recieve the error Virtual Disk Service Error: The specified drive
letter is not free to be assigned. I believe what is occuring is that we used a faulty usb before this attempt and it has
created hidden drives with an assigned C: letter which is why i can no longer change the drive letter.

How would i wipe out these virtual partitions to free up the letter C?

Edit: ive also noticed there are multiple boot managers in the bios

Regards,
Rab