Here are the details I gave monkeyking:
I browsed the interwebs and it seems to be a common problem.
Here are two solutions to try. If you have no luck let me know and we can try a few other things:
1. Turn off your Firewall in the System Preferences, then.
2. Do not select to download All uninstalled media, but rather download them one at a time. By doing this, all of the assets download and install properly.
There seems to be a problem when all the items are selected to be downloaded. Most people say there download gets stuck at 2GB. But if you do the downloads individually it will work.