— a working OSX installation
— your Fusion drive is only 1 partition in Disk Utility (not including the hidden partitions) (ie: not split up, if it is already split this will not work)
— you have no other USB device connected other than keyboard/mouse/USB stick with Windows installer
1) Reboot and do a PRAM reset (when you hear the startup chime hold cmd-option-p-r until you hear the chime again — warning: 2nd chime volume will be blasting loud).
2) Open up Bootcamp assistant and create your bootcamp partition and install like you would normally. Your computer will reboot and proceed with the Windows installer. When you need to select your install partition just select the one called Bootcamp, hit format, the window will refresh, reselect the same partition (should be disk1s4 if I remeber correctly). The formated partition will now allow you to continue your Windows install
The key is the PRAM reset when the drive is only 1 partition in order to clear previous entries that were preventing you to install correctly. If you do that when it is split into multiple partitions it will not do anything and the same error will keep popping.
Also, when you want to remove your bootcamp partition, you dont need to boot into recovery and terminal, you can just go back to OSX, run bootcamp assistant and select «remove windows installation» and it will resize your osx partition to the full fusion drive size.
I have tested this numerous time since saturday and everytime it worked. Between wednesday and saturday, you don’t want to know how many 10s of times I have tried installing and getting that error message 🙂
I only signed up to reply and hope that this info can help others having the same issue that was very very [. ] very frustrating for me this weekend