If you're using a laptop, make sure that your
function (FN) key isn't on. Most of the newer laptops have a
"FN Lock" or
"F-Lock" key to toggle it on/off.
Now if you're not using a laptop, your RO folder might have a version of
LUA files that's
newer than the one currently supported by
heRO's client. If you've installed heRO in a folder with any other servers, I recommend you to reinstall it from scratch (you can find a guide
here).