!!!WARNING!!! I only have proof that this works if your trying to login and play on a wireless connection and only if you are using Vista/Windows 7!
Here's what you have to do. I'll try to be as detailed as possible:
1. Open Control Panel and go to "Network And Sharing Center."
2. In the left hand column, click on "Change Adapter Settings."
3. Locate your wireless adapter and your LAN adapter/Ethernet port.
4. Hold down CTRL and click on each of these. They should now both be highlighted.
5. Now right click on one of them and select "Bridge Connections."
6. After the Network Bridge is created, open Crysis 2. You should now be able to login and play with no issues.
Hope this helps! Let me know if any further detail is needed or if the fix is not working for you.