Bootcamp Issues - Windows Cannot Locate Disc

Hi,

I've recently purchased the new 2017 iMac.

I'm currently trying to install Windows 10 via the bootcamp assistant, everything goes well- I select the amount of data for the partition, I choose the correct ISO file from my desktop which I downloaded from Microsoft directly and my iMac successfully reboots into Windows 10.

Following this I enter my serial key, accept the terms and conditions and Windows attempts to install (I presume). I'm not asked to choose a drive (to format) as I have seen on other tutorials, instead I am met with an error as follows -

"Windows cannot locate the disk and partition specified in the unattend answer file's <ImageInstall> setting. Make sure the setting references a valid partition and restart the installation."

I'm running OS Sierra 10.12.5.

I would really appreciate some input on this issue if anybody can help as I'm really at a loss on what to try next.

Please help! I just want this sorted and installed !

Thank You

Reece