ffmpeg errors

ffmpeg -i Air\ -\ 01\ \[Triad\]\[11ADD24D\].avi -c:v copy -c:a aac -b:v 256k  output.mp4
ffmpeg version git-2012-03-17-d9f26a0 Copyright (c) 2000-2012 the FFmpeg developers
  built on Mar 17 2012 08:48:05 with gcc 4.4.3
  configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-version3 --enable-x11grab
  libavutil      51. 42.100 / 51. 42.100
  libavcodec     54. 10.100 / 54. 10.100
  libavformat    54.  2.100 / 54.  2.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 65.100 /  2. 65.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  7.100 /  0.  7.100
  libpostproc    52.  0.100 / 52.  0.100
[mpeg4 @ 0x9f23d60] Invalid and inefficient vfw-avi packed B frames detected
Input #0, avi, from 'Air - 01 [Triad][11ADD24D].avi':
  Metadata:
    encoder         : VirtualDubMod 1.5.10.1 (build 2366/release)
  Duration: 00:24:10.08, start: 0.000000, bitrate: 1347 kb/s
    Stream #0:0: Video: mpeg4 (Advanced Simple Profile) (XVID / 0x44495658), yuv420p, 704x384 [SAR 247:254 DAR 2717:1524], 29.97 tbr, 29.97 tbn, 29.98 tbc
    Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 48000 Hz, stereo, s16, 160 kb/s
File 'output.mp4' already exists. Overwrite ? [y/N] y
Incompatible sample format 's16' for codec 'aac', auto-selecting format 'flt'
[NULL @ 0x9f41c60] Codec is experimental but experimental codecs are not enabled, see -strict -2
Output #0, mp4, to 'output.mp4':
  Metadata:
    encoder         : VirtualDubMod 1.5.10.1 (build 2366/release)
    Stream #0:0: Video: mpeg4, yuv420p, 704x384 [SAR 247:254 DAR 2717:1524], q=2-31, 90k tbn, 29.97 tbc
    Stream #0:1: Audio: none, 48000 Hz, stereo, flt, 128 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (mp3 -> aac)
Error while opening encoder for output stream #0:1 - maybe incorrect parameters such as bit_rate, rate, width or height