mencoder installed on your server is not able to convert video. You need to look into the mencoder installation.

Code:
/home/spddeluxe/bin/mencoder '/home/spddeluxe/pacorrerte.com/video/big03_2.mpg' -o /home/spddeluxe/pacorrerte.com/flvideo/11923953511950107824.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
If you have mencoder working properly on the server, above command will conver the video file /home/spddeluxe/pacorrerte.com/video/big03_2.mpg to flv format at - /home/spddeluxe/pacorrerte.com/flvideo/11923953511950107824.flv