Unable to find a suitable output format for 'channels'

I got this output when i try to get a video transcoded...

export MALLOC_CHECK_=1; time /usr/local/bin/ffmpeg -v 0 -y -i 'files/videos/original/p6280231.avi' -vcodec flv -b 320k -g 30 -s 320x240 -acodec libmp3lame -ab 64k -ac 1 channels -ar 44100 -pass 1 -passlogfile files/videos/temp/2pass-12 files/videos/temp/12.flv 2>&1 malloc: using debugging hooks FFmpeg version SVN-r19325, Copyright (c) 2000-2009 Fabrice Bellard, et al. configuration: --enable-libmp3lame --enable-libvorbis --enable-gpl --disable-mmx --enable-shared --enable-libfaac --enable-libx264 --enable-libx264 --enable-libxvid --enable-libamr-nb --enable-nonfree libavutil 50. 3. 0 / 50. 3. 0 libavcodec 52.32. 0 / 52.32. 0 libavformat 52.36. 0 / 52.36. 0 libavdevice 52. 2. 0 / 52. 2. 0 libswscale 0. 7. 1 / 0. 7. 1 built on Jul 2 2009 03:50:06, gcc: 4.1.2 20080704 (Red Hat 4.1.2-44) Input #0, avi, from 'files/videos/original/p6280231.avi': Duration: 00:00:26.86, start: 0.000000, bitrate: 2604 kb/s Stream #0.0: Video: mjpeg, yuvj422p, 320x240, 15 tbr, 15 tbn, 15 tbc Stream #0.1: Audio: pcm_u8, 8000 Hz, 1 channels, s16, 64 kb/s Unable to find a suitable output format for 'channels'

i can't really get what could be the matter... please, help me! :)