If you start a proposal and realize that its not going to gain traction, naturally, you'd want to delete it.
Some proposals gain enough traction to prevent that, and the "Sorry, you can't do that" message still relates to SO:
"Sorry, this proposal cannot be deleted: too many existing answers. or upvoted/accepted answers"
While yes, it says proposal, I suggest
s/answers/example\ questions/ in the notification.
Tagging this as a bug, but it isn't really, I'm just not sure what else it could be tagged. Introducing remnant-from-so-on-area51 seemed kind of silly.