unable to parse option value as image size

mars@mars-laptop:~$ ffmpeg -i somemkv.mkv -sn -c:v libx264 -x264opts crf=20 -filter ass=subs.ass -c:a aac -strict experimental something.mp4

ffmpeg version git-2012-12-10-a933698 Copyright (c) 2000-2012 the FFmpeg developers
  built on Dec  9 2012 22:12:26 with gcc 4.4.3 (Ubuntu 4.4.3-4ubuntu5.1)
  configuration: --enable-gpl --enable-libfaac --enable-libfdk-aac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libvpx --enable-x11grab --enable-libx264 --enable-nonfree --enable-version3 --enable-libass
  libavutil      52. 12.100 / 52. 12.100
  libavcodec     54. 79.101 / 54. 79.101
  libavformat    54. 49.100 / 54. 49.100
  libavdevice    54.  3.102 / 54.  3.102
  libavfilter     3. 26.101 /  3. 26.101
  libswscale      2.  1.103 /  2.  1.103
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Input #0, matroska,webm, from '/media/Data/shows/naruto ship/[HorribleSubs] Naruto Shippuuden - 290 [720p].mkv':
  Metadata:
    creation_time   : 2012-11-22 11:04:50
  Duration: 00:23:09.64, start: 0.000000, bitrate: 1904 kb/s
    Stream #0:0: Video: h264 (High), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 23.81 fps, 23.81 tbr, 1k tbn, 47.95 tbc (default) (forced)
    Stream #0:1: Audio: aac, 44100 Hz, stereo, fltp (default) (forced)
    Stream #0:2: Subtitle: ssa (default) (forced)
Codec 0x18000 is not in the full list.
    Stream #0:3: Attachment: unknown_codec
    Metadata:
      filename        : BAARS___.TTF
      mimetype        : application/x-truetype-font
File 'something.mp4' already exists. Overwrite ? [y/N] y
Added subtitle file: '/media/Data/shows/naruto ship/subs.ass' (2 styles, 196 events)
[Parsed_ass_0 @ 0xafbc5a0] Added subtitle file: '/media/Data/shows/naruto ship/subs.ass' (2 styles, 196 events)
[buffer @ 0xafb8a60] Unable to parse option value "0x0" as image size
Error opening filters!