I ran into this yesterday and now again today. I use Threaded View all the time so I see a tree of linked messages.
I read a message in a thread that had been signaled to me by email and it came up OK.
There was a reply to it next on the thread tree and I clicked on the subject entry for it on the tree and it put the URL up in the address box:
http://community.norton.com/norton/board/message?board.id=nis_feedback&message.id=32936
in today's example and after a while Done appeared in the Status Bar at the bottom of my IE7 screen but the page that should appear with the message text and frame are not there -- just a blank sheet.
I can go to the previous message and it comes up OK and today using the Next Message button did not bring up the next message either although yesterday that did bring it up (from memory it was in the TAG thread here) although the URL in the Address box approach did not.
However from Preview on this message, that URL does bring up the text of the message as it should .......
Anyone else run into oddies like this?