Basically when you click new topic on a discussion board, it will scroll up and there is a message saying 'This a community run message board' which is incorrect sentence.
Not to my knowledge. It's common to omit the dash that should be in "community-run". On the other hand, "which is incorrect sentence" is an incorrect sentence.
I believe the OP is referring to the beginning of the sentence there: "This a" where I'm assuming it should be "This is a"--which does indeed appear to be a typo.
And to be more specific, this message shows up in community forums attached to projects, before you post the topic.