This usually means the decoder was installed, but the "splitter" was not. Re-run the installer and ensure all components are selected.
Whether you are a video editor working with legacy files or a movie enthusiast trying to get a specific format to play on your favorite media player, here is everything you need to know about downloading and installing 3ivx. What is the 3ivx Codec?
Right-click the file and select "Run as Administrator" to ensure the codec registers correctly with your system registry.