The startup disk cannot be partitioned or restored to a single partition I have two partitions on my MAC both formatted as Mac OS Extended but only one has macOS on it. When I start the Bootcamp Assistant to install Windows 10 I get the following message:



How to fix this issue? Do I have to erase the other partition?
Yes, collaps the second partition into the OSX partition. After that you have one partition.
Then use Bootcamp to Partition/install Windows