Known issues with Battlefield Vietnam CD Keys:
Invalid CD Key error
This is a common error, and you will get it when you try and join servers. It likely means that something has happened with the registry where BFV saves your CD Key. You can attempt to rectify this yourself by doing the following:
Navigate to your game directory, usually located in: C:\Program Files\EA Games\Battlefield Vietnam or C:\Program Files (x86)\EA Games\Battlefield Vietnam. Once inside your game directory, look for the folder titled "eReg" and go into this folder.
Once inside the folder, look for the application titled "Battlefield Vietnam_code", once found right click on it and click on "Run As Admin". It will prompt you to insert your CD key again. Insert it and follow the prompts.
Once done the issue should be rectified! If not, you can request a new CD Key from us by opening a ticket so we can personally send you one.