Click on Active Topics, then on any thread. Press back button or control-H to return to list of active topics, get an error page about "Another search cannot be performed at this time" (or something like that).
Active topics works through the search function. The search function has flood-control which prevents any single user performing many searches in a short period of time. This is necessary so as to prevent extreme loads on the server.
You can easily overcome this issue:
1. If you are using MS Internet Explorer, hold down [SHIFT] when you click on a link - it will open the link in a new window. When done, close the window and your original window still has the active topic list.
2. If you are using Firefox, you can use tabbed-browsing. Hold down [CTRL] when you click on a link and the page will open in a new tabbed window. Close the tabbed window when you are done, the active topic list remains in the original tabbed window. [CTRL} + [T] opens a new tabbed window in Firefox.