Unable to upload to Arduino Due using version 1.6.8 of SAM tools; bossac.exe throwing an error
I finally figured out the problem. This occurred on both a Mac and PC (Windows 10).

This error occurred because of the true after the -w switch. To fix it I modified the package to tell the IDE not to use that switch.


Go to: %USER_PROFILE%\AppData\Roaming\Arduino15\packages\arduino\hardware\sam\1.6.8 (where %USER_PROFILE% is your windows user directory, for me it was C:\Users\user) in Windows Explorer.
Make a copy of the platform.txt file (I called it platform_backup.txt).
Open the file platform.txt with Word Pad (it had Unix line endings in my environment), search for the string:

tools.bossac.upload.pattern="{path}/{cmd}" {upload.verbose} --port={serial.port.file} -U {upload.native_usb} -e -w {upload.verify} -b "{build.path}/{build.project_name}.bin" -R
This was 3rd line from the bottom for me, and remove the text between the quotes "{upload.verify}". It should now look like this:

tools.bossac.upload.pattern="{path}/{cmd}" {upload.verbose} --port={serial.port.file} -U {upload.native_usb} -e -w -b "{build.path}/{build.project_name}.bin" -R
Restart the IDE so it can re-read the file you just edited. You'll now be able to upload to the Due.