I recently tried posting an answer and got the following error messages:
You must have a minimum of 1 reputation to post on this site.
You must log in to post.
The first issue here is that as you can clearly see in the top right of the image I am logged in and have quite a bit more than 1 reputation on the site. However, I suppose something could have happened to log me out while I was still on that page, and it hadn't been refreshed, so perhaps that is not an actual bug. The bigger issue, though, is that the first error message even exists in the first place.
According to the FAQ on reputation, it is impossible to ever have less than 1 reputation:
No user's reputation may drop below one point; if an action would cause a user's reputation to drop below one point, that user only loses enough reputation to drop to one point (source), and the remaining penalty or loss is waived.
If there is no situation in which one can have less than 1 reputation, why does such an error message even exist? It can't possibly ever be relevant. Now I suppose that if you are not logged in then you technically don't have at least 1 reputation, but in such a case you already can't post because you aren't logged in.
In short, why does the error message about needing at least 1 reputation to post exist?