The Rise of the Witch-king is currently on patch 2.01. If you want to be able to play against other people online, your version of the game has to be updated to 2.01. While the game provides an auto-update function, this does not always work and therefore a manual patch is the only way to update your game to patch 2.01.
For those whose auto-update function doesn't work, the manual patch has been uploaded on the official Electronic Arts site. All you need to do is download it and start it. If even that doesn't work, please proceed to our Technical Support
section and specify your problem there. There are two different versions, one for those who have a CD or DVD of the Rise of the Witch-king and one fore those who downloaded it from the online Electronic Arts Store. You can find the right page below as well as the language you want.