Problem is mencoder on your server not able to convert the video

You can ask your server admin to run following command on server and see if that works (convert video into FLV).

Code:
/usr/local/bin/mencoder '/home/admin/domains/degroenehel.tv/public_html/video/24082007127.mp4' -o /home/admin/domains/degroenehel.tv/public_html/flvideo/1187994234137797706.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 -lavfopts i_certify_that_my_video_stream_does_not_use_b_frames