There are two ways to pull down an update to the MAA.  The online method and the offline method.  If the MAA is in a location where it cannot connect directly to the internet, you may need to follow the steps to update the server via the offline method.  But sometimes even when performing an offline update, you can run into problems.

1.  The MAA is behind a firewall or cannot make outbound requests to the update server.

2.  You are using Internet Explorer to pull down the update (typically evident when you click to update and you don't get any feedback from the browser and no error messages but the update is not being applied.

3.  Your MAA server is not in time sync with the browser

4.  An update has become corrupted.

Make sure that the server has the right time.  If the time is too far off, then certificates will not match up and the update will fail.  Also, if you are attempting to update using Internet Explorer, try using another browser like Chrome or Firefox.

If you have an update that seems to be stuck in the middle, you can try to cancel and restart the update as well.