You have already raised this type of flag.
This only appears in the flag dialog, and indicates to you that you've previously raised that flag type in the past and are not allowed to raise another one of that type again. Basically, we don't want users repeatedly casting the same flag on a post over and over. If the first one got declined, then you either used the wrong flag, need to include more detail to convince us it warranted action, or just plain didn't understand the use of the flag. For the first two cases, it can be useful for the user to flag the post again, but certainly not using the same reason as before.
You have already flagged this post.
This is just a vague message. It actually means you already have an active flag on the post you are flagging. The system only allows you to have one active flag on a single post at any given time, so it won't let you cast another flag until the currently active one has been handled.