"Commands cannot be assigned to that key" on keybind

[Trumpet]

When I did my first party based fight, I realize that my targeting of my party members was not working. Then I realized that F1-3 were not working but F4 was working. When I try to assign F1-3, a red statement comes up stating "Commands cannot be assigned to that key." I tried other keys to be my targeting keys, but I will be most effective if the F# keys work. Thank you.

[Raist]

Not sure on the defaults...but those keys may be reserved for other functions already.

[Trumpet]

Not sure on the defaults...but those keys may be reserved for other functions already.

The default has F1-3 as targeting party members 1-3. This is what I want, but nothing happens when I press those keys. So when I try to change any action to F1-3, it gives the statement in the title.