Had the same issue with Mac OS X 10.10.5 Yosemite, running on a 2011 Macbook Pro. Resetting etc. didn't work so I worked around the problem by installing HX Edit 3.0 on another laptop running on Windows 10. Here the normal update procedures were no problem at all. When connecting my HX Effects to the Macbook again, HX Edit now shows Firmware 3.01 there as well.