Flashing Hucard repro - Uknown 8277

[SpinoDino240]

I'm trying to program one of IchigoBankai's Repro Hucards However I am getting the following when trying to write from PCE -> Flash Repro Hucard -> Write

OSCR HW5 V14.3

[+] PC Engine/TG16

[+] Flash Repro HuCARD

[+] Write
Detecting...
UNKNOWN 8277

I've successfully read the ROM of a few official games but cannot get anything but Unknown XXXX when trying to program.
This is using the AM29F080B, config has #define ENABLE_PCE and #define ENABLE_FLASH, HW5 Rev5.