Boot Camp says "Windows 10 is not supported" on Windows 7 DVD This has been posted on Apple Discussions earlier today, but I couldn't get any answers, so I have decided to also post it here

I have an iMac 27" mid 2011 running Sierra, and I have troubles installing Windows 7 via Boot Camp. I have downloaded the latest drivers onto my flash drive, loaded up the official licensed DVD of Windows 7 Home Premium 64-bit, but when I click "Proceed" after choosing "Install Windows 7 or Windows 8", the Boot Camp Assistant tells me "Windows 10 is not supported. Please use a DVD or USB with Windows 7 or Windows 8", as if my DVD has Windows 10 on it.

I didn't alter the DVD (how could I, it's DVD-R). I've also had Windows 7 previously installed, then updated to 8, 8.1 and 10 via online updates, but after that I have totally wiped out the whole partition and joined it back to Macintosh HD, before trying to perform a fresh install.

Is there a way to fix this and install Windows 7 from this drive?

P. S. I've tried creating a bootable USB with Rufus on another Windows machine, but the Boot Camp Assistant didn't recognize it
After performing a restart (which I have also tried before) the Boot Camp Assistant worked as expected.