Capcom might have been better off releasing their Lost Planet patch a little later with many users now reporting they are unable to stay connected to multiplayer games.
As can be seen in this thread over at the official Capcom website, many people are able to just games, but then receive a "the match host has cancelled the mission, returning to lobby" message only seconds after getting in. A Capcom super moderator for the forums has since replied asking for more information from people and has also said that R&D is working on the issue.
Some people are reporting various "tricks" to be able to play games again, but none of them appear to be a long term fix. Head over to the forum to read up on what's happening, but we'll keep you updated when, presumably, Capcom announce or release a fix for the patch.
