Windows 10 won't install after disk formatting in the installer

Hi all,

I have been trying to install Windows 10 on my 27" 4K with fusion drive running 10.11.4. I followed the step-by-step procedure with Bootcamp Assistant. I have my UBS Windows 10 install prepared, latest updates for Bootcamp and portioned the drive to 100GB. I did this numerous times and can't get pass formatting the Bootcamp partition with in the Windows installer. Each time I click next after format, it say "We couldn't create a new partition or locate an existing one. For more information see the Setup log files".

I can't get past this point after 10 attempts. We time going back to the Bootcamp Assistant removing the partition and creating another. I made a mistake and click the Delete in the Windows installer, think it might allow me to create a new one...and I lost 100GB from my drive..puff.

Help?!!