Solved! After performing a hard reset, holding the reset button until the power light flashes about 30-40 sec then power off the unit, the unit booted up and immediately had the One-step Update offering to update the firmware. After setting an appropriate gateway, One step update did it's thing and I only had to follow the prompts. Firmware successfully updated to the latest version (currently v1.05.52-c1.8.61).
I just purchased an EWS1200-28T (pn #1402A0067300) and tried to upgrade it with the firmware found on the page: https://www.engeniustech.com/engenius-products/managed-smart-network-switch-ews1200-28t/. The firmware link is: https://www.engeniustech.com/wp_firmware/ews1200-28t_fw_1.05.52_c1.8.61_170928-2120.bix. I'm uploading the file using HTTP but after uploading I'm getting the error Illegal Version Format and it quits. I tried downloading the firmware twice in case there was a problem with the download but it's still giving the error.