Brent Simmons has straightforward advice on error messages:
They should be of the form “Can’t x because of y.”
A similar form is this: “Noun can’t x because y.” (As in “‘Downloaded.app’ can’t be opened because it is from an unidentified developer.”)
Badly-written dialog boxes make me lose faith in an app very quickly. Here’s Final Draft 9 when you hit Next on the last element in the Reformat box.
It has the icon for “important warning,” but it’s nothing I need to be warned about. We’ve reached the end of the document. That’s all.
Rather than making you close a new dialog box, the app could place a notification within the Reformat box itself.
Or better yet, do nothing. If you’re at the top of a script and hit Previous, FD9 doesn’t give you any warning. This feels like the better behavior, because you can see where you are anyway.
Simmons also warns against pronouns:
One thing error messages never say is sorry. They’re just reporting, and they respect you enough to know you want the facts, clearly expressed, and don’t need to be apologized-to by a machine.
Also: they rarely (if ever) use the words I, me, my, you, and your.
Here’s Final Draft 9 again:
A better way to phrase it might be:
Can’t delete across a page break because pages are locked.
Getting rid of the pronoun subtly changes the tone: “It’s not your fault, it’s just how things are.”