You can tell that I'm not a good programmer from the fact that I hard-coded the path of the reference volume as ./ref_vols/atlas.img. This causes ROBEX to crash when it tries to register the input volume to the reference (see sample output below). I'll fix this in the next version. For now, the two possible solutions are:
1.Run ROBEX from its own directory.
2.Download the source code, modify the constants ATLASFILENAME, MASKFILENAME, ERODEDMASKFILENAME, DILATEDMASKFILENAME, INITIALMASKFILENAME in RobustStrip.cxx, and recompile.

Sample output when executed from another directory

Step 1  of 9: reading in images... ExceptionObject caught !
itk::ImageFileReaderException (0x112adb0)
Location: "void itk::ImageFileReaderConvertPixelTraits>::GenerateOutputInformation() [with TOutputImage =
itk::Image, ConvertPixelTraits =
itk::DefaultConvertPixelTraits]"
File: /home/eugenio/InsightToolkit-3.16.0/Code/IO/itkImageFileReader.txx
Line: 146
Description:  Could not create IO object for file ./ref_vols/atlas.hdr
The file doesn't exist.
Filename = ./ref_vols/atlas.hdr