You need to check if your concvert command can convert the video to FLV

Code:
/usr/bin/mencoder '/home/espotws/public_html/video/strandgein.wmv' -o /home/espotws/public_html/flvideo/1193650812396910797.flv -of lavf -oac mp3lame -lameopts abr:br=56 -ovc lavc -lavcopts vcodec=flv:vbitrate=500:mbd=2:mv0:trell:v4mv:cbp:last_pred=3 -srate 22050 -ofps 24 -vf harddup
mencoder do not support all the codecs, so verify problem is not with the video you are trying to upload by loading the video to some other vshare sites and see if that works.

If it works on another site and not in your web site, you need to contact your web host, it can be a mencoder installation problem.