There is a question that has been protected, but I would also like to answer as I think my answer can really add to that. Is there a way to answer a protected question?
A protected question is a way the moderators and higher rep users can make sure a post that is getting a lot of attention, say a popular question about a new movie, doesn't get riddled with spam.
The protected moniker disallows anyone below 10 reputation from posting anything on the question. This is so that low rep users can still post a decent answer, but prevents newer accounts typically used for spam and other nonsense cannot.
Seeing your meta rep at 146 tells me that it was some kind of glitch that you couldn't post. If this occurs again, try to get screenshots so that we can bring this to the correct party to get it fixed.