Tweak global settings error message

Created by: Joelkw

Wanted to give the user a little more guidance since I don't know if "global subject" is enough to give them a sense of what's going on – a "settings file" could technically be the native one as well.

(Also a few small stupid english-is-a-dumb-language tweaks, like "a settings file" – only noting this in case you disagree with this overall change, in which case we still should modify the message so "can not" -> "cannot" and "by settings file -> "by a settings file")