Q: Windows 10 unable to locate boot camp partition

I am trying to install Windows 10 on a late 2015 iMac with a 512 SSD.  Using Boot Camp and a Windows 10 ISO, I am able to create the Windows partition in Bootcamp and the iMac restarts into Windows setup. I enter my product key from my Windows 7 DVD and reach the screen showing the partitions.  I select the "Drive 0 Partition 5 Boot Camp" partition and click "Format" as per Apple's support document directions.  The partition is then renamed to "Drive 0 Partition 5".  When I select the Next button, I get the following error message:- "We couldn't create a new partition or locate an existing one.  For more information, see the Setup log files".  The Windows installer does not allow any further progress.  I have erased the partition multiple times using bootcamp and restarted the install and always get the same failure.

Any advice on how to install Windows would be greatly appreciated.  Boot Camp 6 will not let me install Windows 7 on this iMac and so I needed to use Windows 10.  I assume that the Windows 10 ISO downloaded from Microsoft will work with the Win 7 product key and setup appeared to accept it.