Boot Camp Assistant: "This Mac does not support Boot Camp" I have a 2009 Mac Pro (MacPro4,1) which, until recently, had both OS X Yosemite and a Boot Camp install of Windows 10 on it.  Shortly after I upgraded to El Capitan, I found that Boot Camp Assistant refused to run, reporting "This Mac does not support Boot Camp".

Furthermore, I am unable to use BootChamp to reboot into Windows, as it reports a cryptic message "Bless failed".

Any ideas what would cause Boot Camp to stop working?
The solution for fixing Boot Camp Assistant was the same as with previous versions of the OS: reset the NVRAM.

I found a discussion mentioning a similar problem with an upgrade to Yosemite here that I intiially disregarded as it referenced repairing permissions and running a Disk Verify, neither of which Disk Utility appears to support anymore.

As for BootChamp, it is no longer supported as of El Capitan.  System Integrity Protection prevents it from running.