If you are seeing Quicktime error -2004 when looking at an WMV movie embedded in a web page, try unchecking "Create Streaming Movies" on the Movie tab of the Flip4Mac WMV System Preferences pane.
I think this restriction may have been introduced by the Quicktime 7.1.2 or 7.1.3 software updates.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060926041915270