I've followed the instructions to enable the "Create windows 7 install Disk" in bootcamp but I am attempting to install Windows 8.1. How do I force bootcamp to allow me to create a windows 7 or later install disk?
You have to have a version of Bootcamp AND Mac that explicitly supports Windows 8.1. Apple has a knowledge-base article that shows what O/S and Mac supports what version of Windows:
Unfortunately there are some Mac models that just won't support certain versions of Windows. Interestingly (or oddly..) enough the new MacPro and most (many?) of the new Macs only support windows 8.