Q: Unable to install Windows 8.1 or 10 with Boot Camp Assistant

I'm having so many problems trying to install Windows with Bootcamp, I don't really know where to begin.

Firstly, my setup: 2015 5k iMac, 4.0Ghz. 32GB RAM, 3TB Fusion Drive, OSX 10.11.2

I am completely unable to install Windows 8.1 or 10 with Boot Camp Assistant. The version of BCA on my iMac prompts for a Windows ISO file and installs without a USB flash drive (it doesn't give you a choice). It does so by creating a partition for the windows install disk. So I tried running BCA, following all the on-screen instructions and prompts, using a windows 10 ISO from Microsoft. The Bootcamp partition is created and the mac reboots into Windows install. At the point at which you select the partition to install and format it, when you click next it gives an error message "We couldn't create a new partition or locate an existing one".

I've done a bit of digging around online and found that Windows can only be installed within the first 4 primary disks.

When I look at the partitions mine are listed as:

1 EFI Boot

2 Macintosh HD

3 OSX Recovery

4 OSXRESERVED

5 Bootcamp

When you go through Windows Setup and get to the screen where you chose where to install windows to, the Bootcamp partition is ALWAYS disk 5. This is what I think is causing the error. How have people overcome this? I surely can't be the only person having this problem.

The OSXRESERVED partition is the windows install disk, created by bootcamp when you select the Windows ISO. This is where the windows install files come from instead of being put on a USB. However, its getting in the way! I can't delete any of the partitions as they're all essential but I also can't reorder them, and I can't opt to install Windows from a USB.

How have people managed to install Windows via Bootcamp at all?!?!

I've tried to delete the OSX Recovery partition and merge it back in with the Mac HD partition, but I end up losing the disk space once I delete the partition.

I've also tried using Winclone... created the partition in Disk Utility and restored from the Winclone image, however when the restore process finishes I get an error saying "Updating Partition Table Failed" and I cannot boot from it.

WHAT IS THE SOLUTION!? I really do need Windows on my new iMac. I managed to install it onto my old one just fine. How come there are suddenly so many issues?! Please help!