Q: Your disk could not be partitioned !

Let us try the simple steps first, before any major surgery.

Boot in Safe Mode - Try safe mode if your Mac doesn't finish starting up - Apple Support , then boot normally and try BC Assistant again.

What is the version of Windows and what year/model is your Mac?

If you have the 4.0.4033 BC Drivers package on a USB, but do not have a USB driver for Windows, download Paragon NTFS for Mac trial version which will give you read-write access to Windows from OSX. Copy the contents of the USB to a known location. Switch to Windows, and run setup.exe in the Bootcamp folder from this known location.

Uninstall Paragon NTFS once you have drivers installed.

I suggest starting at Use Windows 10 on your Mac with Boot Camp - Apple Support . If you model/year is not listed, my recommendation is to avoid W10, unless you absolutely must have W10 features.

MacBook Pro 15, Late 2011, 2.2 GHZ, inteli7 processor.  El Capitan OS. Like others in this thread trying to install windows 10 on boot camp.  I am receiving the same error message and am at the point of trying to boot in safe mode, but holding space bar after start-up sound and releasing when the progress bar displays, but computer only boots in normal mode.  Any suggestions on how to force a safe mode boot?

You need to hold the Shift key for Safe Mode, not Space bar.

Starting up in safe mode

Follow these steps to start up into safe mode.

1. Start or restart your Mac.
2. Immediately after you hear the startup sound, press and hold the Shift key.
3. Release the Shift key when you see the Apple logo appear on the screen.

After the Apple logo appears, it might take longer than usual to reach the login screen or your desktop. This is because your Mac performs a directory check of your startup disk as part of safe mode.

To leave safe mode, restart your computer without pressing any keys during startup.

If you don't hear a startup chime after pressing the power key, see what to do if your Mac won't turn on.

wow, totally mis-read that.  thanks

Does the Safe Mode and back to normal mode let you start partitioning?

This did not work.  booted in safe mode, confirmed, restarted in normal and received same error message