1.) First, I would make sure you have the current stable release version 25-November-2018 (v1.0.20181125)
 https://github.com/rordenlab/dcm2niix/releases
2.) If that fails, try dicm2nii:
  https://github.com/xiangruili/dicm2nii
3.) Next, are the files you are trying to convert DICOM data or are they Philips proprietary PAR/REC files? I suspect it is a damaged/partial PAR/REC file. In which case you could try to salvage it with
  https://github.com/rordenlab/spmScripts/blob/master/nii_rescue_par.m
alternatively, you can manually fix broken PAR/REC files by editing the PAR file with a text editor. I suspect that the core issue is that your scan was interrupted before acquisition was completed, so the PAR file describes more images than stored in the REC file.