There are so many different codecs these days, supporting different formats of videos and audio. And there are also software trying to overwrite each other during its installation on your computer. It is not uncommon to find out one day, when you try to play a video file in certain format, the computer complains a specific codec is missing.
Normally you can reinstall the software that supports the missing codec and the problem should be fixed. In this case that I would like to talk about, the missing codec is the Windows Media Series 9 codec (WMV3). The codec is included when you install Windows Media Player. Alternately the codec is downloaded from the Microsoft site when a video file of this format is first played.
In some rare cases, Windows Media Player cannot and will not automatically download the codec. And there is no common software you can install to get the WMV3 codec. A solution is to uninstall the current version of Windows Media Player (in this case, version 11) and rollback to the previous version. When the old version plays the first file with WMV3 codec, it will download the codec from the Microsoft site. Once that’s done, you can upgrade the media player back to the current version.