Video Conversion issue to WMV using FFMPEG

Hi Friends,
I have developed the silverlight player that plays the WMV file. Now, visitors will upload any popular extension from the website. I would convert the files to WMV using ffmpeg. The problem is that the conversion to WMV goes fine. But it is not playing in the silverlight player I developed. It is not even playing in Windows Media Player (huh). and it is playing fine in VLC media player.

Please anyone help me..,
thanks..,