Try downloading it with another program, or post the link to the content.
Instead of flvextract, you can also try ffmpeg & mp4box (using three steps) to demux the flv:
Code:
ffmpeg -i "filename.flv" -vcodec copy -acodec copy "filename.mp4"
then, take "filename.mp4" from above and do these two steps with
mp4box to demux the x264/avc & aac:
mp4box -raw 1 "filename.mp4"
mp4box -raw 2 "filename.mp4"