Hmmm, ok, this is a little out of my realm of expertise here, so I went and checked the web site and did a bit of poking around. I first checked under "Codec issues" and came up with something about the error message you got. Does this help at all?
The Player displays an "error downloading codec" message. What can I do?
When you select the option that specifies that the Player download codecs automatically (see the previous question), the Player may try to download the codecs required to play the file. To ensure successful download, make sure that:
• You are using Windows Media Player 7 or later.
 
• Internet Explorer 3.02 or later is installed.
 
• The Internet security setting in Internet Explorer is set to Medium.
 
• You are connected to the Internet while the file is playing.
 
Additionally, if your computer is running Microsoft Windows NT, Windows 2000, Windows XP Professional, or Windows Server 2003, you must be logged on as an administrator or as a member of the Administrators group. If the computer is part of a network, your network administrator may prevent codecs from being downloaded to your computer. If you still get this error after you have taken all the steps to ensure a successful download, contact the network administrator for assistance.
If you still get this error, the codec server may be temporarily unavailable (in this case, try to play the file again later) or you may not be playing a Windows Media file (see the next question).
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The Player displays a "missing codec" error. What can I do?
The Player has tried to automatically download the codec from the codec server, but the codec is not available. Typically, this error message is displayed if the required codec is a non-Microsoft codec. Because codecs are constantly being created and improved for a variety of digital media formats, it is common to not have the necessary codec.
For more information about finding non-Microsoft codecs, see the question, "How do I find a codec?" in the Top Questions about Codecs in Windows Media Player Web page.