Can't boot into Windows from external drive

I have used Winclone 7.1.1 and chosen Volume to Volume cloning to make a clone of my existing Bootcamp partition onto an external USB drive. The clone completed successfully however when I try boot into windows from the external drive it shows the Windows loading screen but then shows a blue screen with some info and reboots. I am using windows 7. Are there certain steps I need to follow? Does it matter that my internal drive is still installed and has it’s own version of bootcamp on it?

What model of Mac is it? External booting works most reliably with Windows 10 and EFI booting.