inCrysis received official word on Crysis multiplayer issues. Workaround is also included.
"We just would like to let you know that we are aware of the currently occurring issues regarding playing Crysis Multiplayer online. We are already in touch with Gamespy, EA and the world-wide server provider to resolve the problems. This topic has the highest priority for us now and we hope to come up with a solution as quickly as possible.
What we figured out so far already is that when you uninstall the MP Beta/SP Demo after you have installed the full version of Crysis your CD-Key might get removed accidentally. If this is the case please have a look at the workaround we provide further below. There is no guarantee that these work, but they have been helpful to many out there already."