Windows 10 installation fails on can't tell if your PC has enough space

Hi
Have trawled through previous threads and not yet found this one.
I am at my wits end with this. I am using parallels 11 latest version. I have tried upgrading my Win 7 to Win 10 via the mediacreator download 9as recommended by parallels) and also via a USB stick. In all cases installation fails with
'Something happened. We can't tell if your PC has enough space to continue installing Windows 10.Try restarting setup'
Restarting setup gives the same. Rebooting mac and VM gives the same. I have cleared disk space so VM is set to 100GB with about 50G free and my memory is set to 2.2GB for VM. I am using a macbookair with 4G installed RAM.
Installation is not saying I don't have enough RAM or disk, rather that it cannot tell if I have.
Any ideas - I have been trying this for months with no solution.
Steve

 

To upgrade Windows 10 virtual machine refer this steps.

 

I've done all that (sorry, I thoiught that was clear in the question). I have followed the (limited) parallels installation help.
I have checked for file errors (sfc), my updates are all fully competed, only Windows 10 appears as an update.
I get past the license terms and I get the above error message when the installer is checking machine is OK for installation. I don't get to the last two images in yhe help page you refer to.
Goes through license, getting updates, checking what to keep, Making sure your PC has enough space..... then says we can't TELL if your PC has enough space to install windows 10....

 

Been through that, checked sfc and all windows updates. Nothing there helps I'm afraid. It seems like windows installer can't determine disk space or memory or something similar.
Memory allocated (in parallels config) is 2.2G, Windows hard disk is 100G with about 50G free and the System reverved partition is 350M (using partition wizard as suggested).

 

Report submitted 102991671
Steve

 

Note that I have also tried resetting NVRAM and that has no effect either.

 

Hi StephenK1,
The reason for this happening is because Windows updates were not installed properly. So the first thing you should do is to check for Windows updates using this Microsoft Fix it tool and run the sfc /scannow command.

 

Done that already. Both fixit tool and sfc. In my answer a few steps back
Steve

 

Hi StephenK1,
If the above solution doesn't work, please contact Microsoft--this issue could happen on real PCs, too.