Why cant you connect to WoW after downloading patch 3.3.5

As of the time of this writing (23/10/2010), patch 3.3.5 is only released on US servers, and because of this the servers have an extended downtime. If you are using a European client, trying to install the US-only 3.3.5 patch will result in an incompatible game version. If you are using a US client, it means you will have to wait for servers to come back online.