I just tried a Win install with the same setup and had no problems. This time I didn't remove the ISO, it stayed connected the full time. So maybe we are missing an option or doing something slightly different.
When I install Windows, I choose the Custom install. It shows the hard drive as being a 32 GB one (even though we know it's only 2 MB).
When you boot up the VM, does it ask you to press a key to boot from the CD or DVD? If so, the ISO is still connected some way or another. How did you disconnect the ISO?
How much free space on your host hard drive do you have? In the VM that I just installed, it took up 9.3 GB (dynamically allocated). I skipped the Windows Update part as it was taking too long. It would be larger with the updates.
Consider trying a fixed size VDI. 30 GB is about the minimum that you want to go. Why? Because Windows + (just a few programs) + Major Updates you'll need about 30 gigs total to update. I've had a 30 GB VM running a year or two now and it's been though several major Windows Updates. If you want to install more software, consider a larger drive.
How much total RAM do you have (on your real system) and how much did you allocate for the VM? The Guided setup automatically chooses 2GB (which is the minimum required for 64-bit Win10). That's how much I used on the VM that I just installed.
I'm also thinking that this may not be a VM problem at all, but maybe a Win 10 setup problem.