Have you tried deleting it using Disk utility?I'm running the latest Beta of High Sierra and I would like to delete my Boot Camp partition to get more space on my HD. The Boot Camp assistant does not work and I get the following error message. Does anybody have an idea? Thanks!
Wait what exactly do you mean by that? because I have a windows partition as well but it thinks thats the main partition.What works is to transform the Boot Camp partition to an APFS partition with Disk Utility and use it within Mac OS. Disk Utility just won't merge it to a single partition with the Mac OS partition.
My problem was that I wanted to get rid of my Boot Camp partition and merge both partitions into one again without reinstalling macOS. The Boot Camp Assistant didn't let me do anything and gave me the message I posted in the beginning. So I tried the Disk Utility tool and I could reformat my Boot Camp partition to an APFS partition right away or delete it first and format it afterwards. Either way worked on my 2015 13-inch MacBook Pro.3.1 i7. I still cannot merge both partitions but I can use the old Boot Camp partition as a separate HD now.Wait what exactly do you mean by that? because I have a windows partition as well but it thinks thats the main partition.