I am having the same issues as the individuals above. The firmware update gets to 99% and fails. I am installing your firmware on a WF-4734 printer using the USB cable. I use this printer with my Omen Hewlett Packard workstation strictly with the USB cable. I have not experienced any issues printing content unless the cartridges were empty. In this instance all the cartridges are full with the exception of the 802XL Black cartridge and it is at 50%. The reason for the firmware change is I hate having to change out color cartridges just to print in black and white. Also, I could be mistaken but I think I heard that Epson changed their firmware to not allow non Epson updates to be applied. Have you heard this? Could this be the reason your firmware will not work with my printer? The firmware on my printer was recently updated by Epson and is now displaying version CM27J5.
Just to be clear, I power cycle the printer and then try to apply your firmware update. I have done this twice with the same result. I do not touch the printer at anytime during the update.