Look like requirements installation is not proper.

Run following command on command line and see if it works.

Code:
/usr/local/bin/mencoder '/home/amattube/public_html/video/mahsdg.wmv' -o /home/amattube/public_html/flvideo/4ca4238a0b/1260817801686090519.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