That is very odd. If you could please PM me the file I'll investigate.Selecting .binds file "%APPDATA%\Local\Frontier Developments\Elite Dangerous\Options\Bindings\Custom.3.0.binds" for use with generating a ref sheet on edrefcard.info when I get this error:
Incorrect file supplied; please go back and select your binds file as per the instructions.
Which say to get them from the %LOCALAPPDATA%\Frontier Developments\Elite Dangerous\Options\Bindings\ directory.
Edit: edrefcard seems to work fine with a Custom.2.0.binds file from 8/12/2017, but not with a Custom.3.0.binds file last modified as of 6/29/2018.