I’m pretty sure that “0” is the default value for “mayChange”–in other words, that “mayChange = 0” is effectively in place if you don’t specify otherwise. The error seems to be complaining that “mayChange” has the value “0”, despite a change being requested.
In other words, if you are changing an OnscreenText, the solution would presumably be to give that specific object the parameter “mayChange = 1”.