The answer is almost in all likelihood the user is trying to do the upgrade with El Capitan as the Mac OS. El Cap has SIP, so the system integrity protection is preventing a change to the system that could harm it. Disable SYSTEM INTEGRETY PROTECTION. do a google search for proper way to do this. your going to go into TERMINAL, make sure your familiar with how it works. CSRUTIL disable. Didn’t work? you didn’t follow the 4th sentence!