Answer to "Error 5570 when using the upgrade tool 4.1 to 5.1"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!
Answer to "4,1 to 5,1 Firmware tool saying no internet access Solved"I can confirm that the issue, if you have ruled out all possible chances your internet is actually not working , is in the router. I went loco with this !