Greetings-- I wanted to follow up on this topic, because I'm having the same problem. My workplace is running Archon 3.21, and I'm using Google Chrome 21.0.1180.83 m on Windows 7. The same issue also occurs in Firefox and IE, though: I can't get the menu to expand beyond the series level, even though child content exists.
My co-worker who administers our Archon services has tried to tinker with user rights and so forth, but so far to no avail. I also seem to be the only one around here reporting this error, so I'm relieved to see something similar has happened somewhere.
Thanks in advance for any help in resolving this issue!