To all those getting prompted to re-download assets, this is NOT necessary unless the assets are missing or just messed up. The code that keeps track of downloads has nothing to do with rebuilding the database. If everything is working correctly either just ignore the downloader or right click on items and choose Remove selected. That removes items from the list but doesn't uninstall it from your game. If you download items twice you might end up with more than one set of the packages for the items of DLC. This just wastes hard drive space and can cause the dreaded Payware Installed but not active error.
William
Thanks for your tip William.
This level of advice should not be necessary for purchased products like this though! This is all getting very silly and disappointing. Like many others, from now on I'm not going to upgrade/download any content updates from N3V until long after it is issued.
What is the fix if the "Payware installed but not active" issue does occur? Delete everything and re-download - a third time in as many days?!