Westwood online support library is missing or invalid

On certain version and distributions of Tiberian Sun you might encounter the following error:

Westwood online support library is missing or invalid

This error is caused by issues with your Westwood internet components installation or registration. Follow these steps to fix this error:

1. Make sure you have the TFD freeware version installed. The freeware First Decade version of Tiberian Sun comes fully patched and includes both Tiberian Sun and Firestorm. It is also bundled with a few patch files that set you up for online play so there’s no reason you shouldn’t be using it at your main installation of the game. You can get the First Decade version from one of the links here.
2. Make sure the game is installed in the right directory. The First Decade version of Tiberian Sun expects to be downloaded in C:\Program Files\. Your full game path should be as follows:
   C:\Program Files\EA Games\Command & Conquer The First Decade\Command & Conquer(tm) Tiberian Sun(tm)\SUN
If you don’t have the game installed in this directory the included shortcuts and registry patch will not work. You can simply move your extracted EA Games folder to C:\Program Files\ if it isn’t there already.
3. Run registerWOL.bat. Navigate to your C:\Program Files\EA Games\Command & Conquer The First Decade\Internet directory and double click registerWOL.bat. You should get two messages that the installation succeeded. Now when you start the game you should be able to go online.

There is a chance that this won’t work. Specifically, after running registerWOL.bat you may get the following message:

The module "WOLAPI.dll" was loaded but the call to DllRegisterServer failed with error code 0x80020009

This means that the script failed to run. In this case you’ll probably have to register these DLL files manually instead via the following command prompt commands:

cd "C:\Program Files\EA Games\Command & Conquer The First Decade\Internet"
regsvr32 WOLAPI.dll
regsvr32 WOLBrowser.dll

If you’ve followed the above steps and are still experiencing the Westwood online support library is missing or invalid error, please post in the comments below. To increase your chances of a solution being found include as much detail as possible (which version of the game you’re running, what operating system you have, what video card you have and steps to reproduce the issue). Screenshots are also very useful!

Sources: link 1, link 2, link 3