Some users have reported they are not able to download updates. The 'Search for updates' reveals updates, but they cannot be downloaded. Often a 'HTTP Error 403' or 'bad checksum' is displayed. This has a simple reason - thousands of people trying to download from the default server, which can't handle such a load. If you try again, have a second look at the menu bar. It has a pull-down item to select a mirror. Click the arrow beside it, and select a different location, where you'll most probably have better chances to download.

Current problems with the main installer download have the same reason - the servers not being able to handle such large amounts of downloads. Even the University isn't able to deal with many thousands of downloads at the same time. Please have some patience; more mirrors are being added again.