You don't have to register, just type in an username (max. 8 letters) and a password (exactly 8 letters if I remember correctly) and click OK.

You can alternatively set up a Hamachi (VPN) connection with other players and play using it.

Are the Westwood Shared Internet Components installed? If you already have Tiberian Sun (or Red Alert 2) installed on your computer, you'll likely have it installed already; if not, you can either install the Shared Internet Components from Tiberian Sun's or Red Alert 2's installation disc or you could download the Westwood Shared Internet Components installer to install it separately.

Well from the very beginning I had a log in and password that where both 8 characters long and they didn't work.

I download the Westwood shared internet components but there still seems to be an error going on.

In fact it says DOA has experienced an error and suggest I should come to this site to download the latest version (I already have the latest version by the way).

What operating system are you using? If you're running Vista or Windows 7, try running DTA as administrator and if that doesn't work, try disabling user account control.

I'm running Windows XP Home edition.

I currently dont have any C&C games installed, just DTA, I ran the exe of the link you provided for the westwood shared internet components.

Does the link provide everything of the shared components?

I can probably take a screenshot of the error if you want.

I'm guessing you're getting an internal error; if so, you don't need to upload a screenshot.

The Westwood Shared Internet Components Installer I linked you to should provide everything you need to be able to play online, but I haven't properly be able to test it myself (considering I already have them installed).
You could try to download and install Tiberian Sun (just google it; it's freeware now after all) and see if you can get online with that.

Here's an installer for the Westwood Shared Internet Components which has been proved to work multiple times: http://xwis.net/downloads/WOLAPI-0.0.0.exe

If that doesn't work, then you could try downloading Tiberian Sun and seeing if you can get online there (as Bittah adviced).

Ok, I installed my copy of Tiberian Sun and downloaded the patches, DTA finally works online.

Thanks for the help guys.