Using dcm2pnm to convert a DICOM image I get the following error message:
ERROR: invalid value for 'PhotometricInterpretation' (LittleEndianExplicit)

[This only applies to systems where the data dictionary is not built-in but loaded from file (typical for Unix systems).] Most likely the environment variable DCMDICTPATH is not set-up properly. Please note that it needs to point to the data dictionary file, not to a directory (see also older entries below).