Cmus does not recognize all of my media files

[Zapata]

How come that cmus does not import all of my mp3 when adding them by ':a ~/Music/ACDC/'. Of course this directory contains music and is not empty and it plays my music with other mediaplayers such as rhythmbox, amarok etc. This happens only with a fiew music files (mostly mp3) but i don't know what to do to make cmus adding all of my music to the library. By the way i can play this music from browser view (5) but it just won't appear in view (1).

Running Ubuntu 12.10
cmus v2.4.3

$cmus --plugins brings me to:
Input Plugins: /usr/lib/cmus/ip
  mad:
    Priority: 55
    File Types: mp3 mp2
    MIME Types: audio/mpeg audio/x-mp3 audio/x-mpeg
  aac:
    Priority: 50
    File Types: aac
    MIME Types: audio/aac audio/aacp
  vorbis:
    Priority: 50
    File Types: ogg
    MIME Types: application/ogg audio/x-ogg
  flac:
    Priority: 50
    File Types: flac fla
    MIME Types:
  wavpack:
    Priority: 50
    File Types: wv
    MIME Types: audio/x-wavpack
  wav:
    Priority: 50
    File Types: wav
    MIME Types:
  mpc:
    Priority: 50
    File Types: mpc mpp mp+
    MIME Types: audio/x-musepack
  modplug:
    Priority: 50
    File Types: mod s3m xm it 669 amf ams dbm dmf dsm far mdl med mtm okt ptm stm ult umx mt2 psm
    MIME Types:
  ffmpeg:
    Priority: 30
    File Types: ac3 aif aifc aiff ape au mka shn tta wma aac fla flac m4a m4b mp+ mp2 mp3 mp4 mpc mpp ogg wav wv
    MIME Types:

Output Plugins: /usr/lib/cmus/op
  pulse
  alsa
  ao

Would be nice to get it working!

Zapata