Users can't see comment box after logging in

Hello,
I am using WP 2.8.4 on my company’s web site for blogs. Because of horrible limitations of our hosting provider, I cannot upgrade to 3.0 (page file size limit of 8mb).

We require registration, and it was working fine at first, but now some users are having trouble – especially on IE. When they log in, it takes them back to the blog post and doesn’t show the comment box – it has the same login line. It’s like the page isn’t refreshing correctly. When they go to a different blog post or Shift+refresh, it usually works.

I have rebuilt and re-uploaded fresh versions of my wp-config.php and wp-login.php files (made sure to delete from the remote server first). I have removed all plugins, eventually putting two back on because it didn’t help. I’ve played with the WP admin settings and nothing seems to help. I’m at my wits end with this. Any suggestions?