can't update firmware on RT-AC52U

hi,

i have updated the firmware on the RT-AC52U many times before, but this time it seems to work, but it doesn't.

i currently have 3.0.0.4.380_8457

i am trying to update to 3.0.0.4.380_8497

i DL'd the file, unzipped, and upload to the router. it all seems to work and then prompts me to manually reboot. i turn off, unplug, wait, turn back on, no joy.

any ideas??? thx.