This pane is supposed to show the main document that was chosen. If you can see this instead, and the file isn't still loading, that didn't happen.
If you entered the url for makeframe.html directly, this is what you'll get. You probably meant to use mainframe.html instead.
To use makeframe.html, give two arguments like so:
infodoc is the URL of the document you want to appear
in this space, and
indexdoc is the URL to put in the left pane.
If you used a url of a document in this set, e.g. message_tap.html, then that document will invoke makeframe.html to put itself together with the proper index page. Somehow, that process started but did not complete.
I've seen this happen in Microsoft's IE6 when the file is served locally. If the url is a file, rather than a web host, then it ignores the stuff after the '?' on the address line! It's rather flakey in what it takes for a filename, too.