I had some trouble with this myself, so i thought, maybe I can help others with the following:
First off, you need to have Punk Buster running before you can join a server, and punkbuster only runs on 32 bit
If this is ok and you still got a error, please press ~ (for console), on the console you can find the real error.
if it says that your CD-key is invallid, please use the key changer located on your crysis CD (tools/Crysis_code.exe)
If punkbuster needs to be...
How to get MP working...
First off, you need to have Punk Buster running before you can join a server, and punkbuster only runs on 32 bit
If this is ok and you still got a error, please press ~ (for console), on the console you can find the real error.
if it says that your CD-key is invallid, please use the key changer located on your crysis CD (tools/Crysis_code.exe)
If punkbuster needs to be...
How to get MP working...