If your game has been updated to version 1.03 (for Steam and EA app users), you will no longer be able to play online.
To play online again, you must downgrade to version 1.02.

You can do this by deleting the following file:
C:\\Program Files (x86)\\Steam\\steamapps\\common\\Command and Conquer 3 – Kane’s Wrath\\CNC3EP1_YourLanguage_1.3.SkuDef

Then, reinstall the community patch and rehook CNC-Online.
If you don’t know how to do this manually use the Standalone Downgrade1.02 Installer.