Activision have acknowledged that there is currently a problem with the Master Server returning valid IDs for newly started dedicated servers. At the moment, it is taking upwards of 15 minutes for the ID to be populated in the server browser, and for players to be able to connect to it. Recently, the whole Master Server was offline, and it was not possible to populate a browser at all. Today, however, the Master Server is back up, but the length of time it takes to return valid IDs for new servers is still taking a long time. They have said they are working on it.
I'll updtate this as and when I get more info.