"Discussion Frozen" - What does it mean?

I'm still very new to Steemit and I guess will go through the learning process just like anyone else new. However, I just spent a good while reading a series of 3 articles by Eric Vance Walton (I think that is his name) and went to post a comment. I spent a good few minutes trying to compose a valuable and thought out reply that was worthy of the work that Eric had put into his original post but was then met with the words...

"Discussion frozen". As someone new to Steemit, I can see why that would potentially put someone off of the platform if they didn't know any the wiser.

I have no proposal, but does this need a re-think? Any suggestions on how this might be improved. We surely want people to engage and create great content and help improve the group/crowd if that's what it's called.

Anyway, hope for some feedback so 1) I can learn 2) I can help contribute to make Steemit a better place.

Thanks. Paul.

Oh, one more thing, I took a screenshot which is on my clipboard and would love to be able to just post it in this article, but I don't seem to be able to do that either, so any tips gratefully received. I am on a desktop, not mobile.