So, I think from your comments you're mistaking "answers" for "comments" and vice versa.
To comment on any post that isn't your own, you need 50 reputation points; this is a restriction within the system itself. You add these with the "Add a comment" link underneath posts.
Answers are the big text box underneath questions where you can add answers. These must be answers to try and solve the OP's question or resolve the OP's question. These are NOT for comments, and not for "works for me" or "did you ever figure this out" or "me too" type posts.
If you were attempting to answer a post, then in this case, you were attempting to answer a protected question before you had sufficient reputation.
Protected questions give you a notice on the question itself that the question is protected. It looks like this:
However the answer you posted to the question initially was a comment and not really an answer, so it was deleted; you then needed to get to 50 rep for comments. (I converted your answer into a comment though, so it does show up as a comment)