The problem with inkey is that it isn't part of the acknex.dll (from http://www.conitec.net/beta/ainkey.htm) as it uses wait (and thus the lite-c scheduler) !

simulating inkey shouldn't be that hard, I guess the description of inkey in the GameStudio manual offers a reasonable solution :
You could use wait and check a variable that contains the value of the last pressed char, for example the engine variable key_lastpressed !