I was going to tell you to check https://Steemd.com because Steemd could tell you how many resource credits (RC) you have. Sometimes, if I don't have enough RC for about ten comments, then I can't comment or post something that is too long or longer. In other words, longer posts and comments cost more RC.
But I looked at your RC on Steemd and it says you have enough RC for 100 comments. So, I'm guessing that is not the problem. Maybe somebody else knows what is wrong. I don't think it is a posting key problem. If you log in with your private posting key, then you should be able to comment and post.
Yes, there is a limit to posts. I save my posts in text files just as a backup. If a file is larger than about 48 kilobytes (kb) or around 8,000 words, then I get an error. I'm guessing that is too big. So, then I make it smaller. Then it lets me post it.
It is around 4,000 words now. They need to fix the error message, just say, your post is to damn big trim it down.
Are the blocks smaller? I think that the posts are saved in blocks like Bitcoin but maybe different. Yeah, they should make the error message say things like that. We got to make the error messages as simple as possible before millions of more people join Steemit, which they will be doing.