Yes, I am registered at that site and can log in from my "trouble" computer. I can visit different pages of the site. As I said, it is a newspaper, and there is an area for posting responses to each article. From other computers I can post replies, but from my laptop I cannot.
I can post at other sites (this one, for example). I actually have no trouble with any other sites and I can get around that newspaper site just fine - I just can't post on that site. When I type something in the comment box it shows, and when I hit "add reply" it looks like it is going to post...the site reloads, but the post doesn't show up. As I said, it works properly from other computers.
I have contacted the website editor, and he doesn't know what's wrong. Apparently the newspaper is part of another news system and the local guy doesn't know the tech side. Maybe I need to ask him how I can be in touch with someone in the systems tech dept.
Very strange, I think, and I was hoping someone would have some idea of what the problem might be.
Thank you to those of you who have replied.