gdal - How do you open shapefiles with ogr2ogr

I'm following along the D3 tutorial, and on this line:

ogr2ogr \
  -f GeoJSON \
  -where "adm0_a3 IN ('GBR', 'IRL')" \
  subunits.json \
  ne_10m_admin_0_map_subunits.shp

run into the following problem:

FAILURE:
Unable to open datasource 'ne_10m_admin_0_map_subunits.shp' with the following drivers.
  -> ESRI Shapefile
  -> MapInfo File
  -> UK .NTF
  -> SDTS
  -> TIGER
  -> S57
  -> DGN

  -> VRT
  -> REC
  -> Memory
  -> BNA
  -> CSV
  -> GML
  -> GPX
  -> KML
  -> GeoJSON
  -> GMT

  -> PCIDSK
  -> XPlane
  -> AVCBin
  -> AVCE00
  -> DXF
  -> Geoconcept
  -> GeoRSS
  -> GPSTrackMaker
  -> VFK
  -> PGDump

  -> GPSBabel
  -> SUA
  -> OpenAir
  -> PDS
  -> HTF
  -> AeronavFAA
  -> EDIGEO
  -> SVG
  -> Idrisi
  -> ARCGEN

  -> SEGUKOOA
  -> SEGY

I have the .shp, .shx, .dbf, and .prj files all in this directory. Why is ogr2ogr unable to read them with anything? (Shapelib is installed.)

I'm using Ubuntu 12.10 if that makes any difference, and had to compile GDAL from scratch, using version 1.9.0.

Answer

I don't know the formal answer to this question, and I'm unable to provide more details of what was going wrong, or what was done to fix it. However, strangely, it started working again.

In response to Dave X's comment above, I'm going to accept this as the correct answer---since I won't be able to provide additional information that will lead to adequately solving it.

If you're in the same position I was at the time of asking this, I can only advise you to keep re-installing all the stuff you've already installed several times, reboot occasionally and hope.