diskpart is a windows utility to zero out a drive. It can delete partitions and MBR so the drive is completely wiped of Windows information, which prevents Windows from mounting it. Then WinUAE can have full access to it.
https://technet.microsoft.com/en-us/library/cc766465(v=ws.10).aspx
You want to 'clean' the disk but make absolutely sure you are working on that disk and not one of your windows disks.
Make sure you use 'list disk' to find the appropriate disk/cf card and then 'select disk' to change the focus to that disk. all commands will be directed to the disk currently with focus.
I have the exact same reader. Sometimes even with cleaning the cards get stuck in some odd mode, where it refuses to be detected after it tries to RDB it in WinUAE.
Its also worth noting to make sure WinUAE is running as Admin (right click exe and click "run as admin").
