im trying to play multiplayer and its saying invalid CD key

Try aksing the GoG staff. Maybe they can give you a new CD key!

The official multiplayer servers for Empire Earth were shut down in November last year, and that's why you're getting that error.
You can still play it online using GameRanger. There are quite a lot of EE1 players still out there.

so are the games GOG sell, like a ripped game? Because i can't host any type of games saying it has an invalid CD key, and also when I try to patch the game. It says it cant identify the version of the game.

No, they are not ripped games. According to ScottKevill, you can't host games on-line (I suppose you don't mean LAN games) because there are no servers for EE anymore.
As for patching, of course it can't identify your version because it's already patched to the max.
EDIT: I've just read in the other thread you have problems connecting on GameRanger. Have you ever asked GOG for a unique CD-key? AFAIK, you have to do this with games that require CD-keys if you want to play on-line.

yeh, I just sent a request for a CD-key. I hope i get a reply sometime soon. THank youj

See here
http://www.gog.com/en/forum/empire_earth_series/cd_key_entry_ee1

Is this the official thing to do?

Myself and several of my friends recently purchased EE1 from GoG specifically for the purpose of playing multiplayer tonight. We're currently trying to test it out now and I'm getting the "invalid CD key" error.

Aren't all GoG games supposed to be DRM-free?

I just bought the game and installed it. Went to multiplayer to play with my friend and it said INVALID CD KEY. When I bought from GOG they never gave me a key just the download I need help.

I will re-post this so others can see this and so they can play.

The following can be found here: http://www.gog.com/en/forum/empire_earth_series/cd_key_entry_ee1

What you need to do is go into your empire earth folder and edit the file WONlobby.cfg then change the value CDKeyCheck from true to false. This will allow you to play LAN games.

"Direct connection" games also work after that. Under Win7, I had to go to the control panel, Windows Firewall settings, then click on Advanced settings. Selecting "Inbound Rules" in the left-hand panel showed me a list of rules for individual programs, including two for Empire Earth which I had to toggle to allow them. After that I was able to host a game and play with a friend.

Hi trademark: I just with through this when I attempted to play a LAN multiplayer with my son. Although it took a while to find it, this solution worked for me:

Find the installation folder (probably something like C:\Program Files\GOG.com\Empire Earth Gold Edition\Empire Earth - The Art of Conquest).

Edit the WONLobby.cfg file and change the line that says:

CDKeyCheck: true
to
CDKeyCheck: false

Save the file. You may have to fuss a bit with permissions (save elsewhere & copy it back into the folder) depending on the security settings of the folder and which OS is installed. Also ensure the firewall is set to allow the program through on both ends.

This resolved the issue for us and we can now enjoy multiplayer.

Thank you very much!