http://wiki.jriver.com/index.php/Updates
Right. The Wiki article covers it pretty well.
However, essentially the deal is this: JRiver releases a new build on this forum roughly once per week. This is what corresponds to the "Latest" update channel using the built-in auto-update system.
These are moved to the "download page" and the "stable channel" auto-update periodically. This division is essentially to allow users to use MC without being bombarded with constant update available notices. However, if you ever have trouble with anything, step one would be to come to Interact and download the most recent version from here (or set the Auto-Update system to "Latest" if you don't mind being bothered).
The current version on the "Stable" download page is actually pretty old right now because they made some fairly radical changes to the underlying technologies in MC. This was now quite some time ago, and the current builds are stable for most of us, but I think JRiver is letting it "settle out" a bit longer before they push a new build to that spot.
Hopefully this makes sense.
In any case, if you update to the current version from Interact, it should sort out your problem.