Covert error is due to mencoder is not converting the video to FLV format.

This can happen due to problem with mencoder or if the video format (codec used) is not supported by mencoder.

Check templates/debug.txt file, you will see the convert command. Ask your host if that convert command works on the server. Mencoder have recently changed the convert command, if you check vshare include/settings/video_conversion.php file, you will see two commands, one for old and other for new version of mencoder, try both.

If none works, it can be a server problem. Ask the host what convert command works on the server.