Hi Venkat, Thank you for the information. I have to ask a few more questions though as I unfortunately cannot get this to run on my Mac test system. Are you using the Mac OS X gfortran from http://r.research.att.com/tools/, MacPorts, HPC, or Fink? I am using the one from http://r.research.att.com/tools/, as this is the only one that can compile the Python Scipy package. Would you happen to know the exact version, as GCC has renamed the old libgfortan.3.dylib file to libgfortan.2.dylib in the current releases hence I might need to hunt down an old version to make this run. For the Linux systems, Art Palmer's binaries are compiled only for i386 using both the old g77 and pgf fortran compilers (in the gnu/ and pgf/ directories respectively). I cannot run the pgf version as it segfaults (it was compiled on Linux 2.2 and doesn't seem to run any more), but the g77 version compiled on Linux 2.6 runs fine. Do you know which of these two binaries you are running? Are they self compiled or Art's binaries? The commands 'file' or 'ldd' followed by the modelfree4 binary will give some useful information. On my system with the g77 binary, unfortunately I do not see the same problems as you do. This is a difficult problem because for every Modelfree4 binary variant which gives a different result, I have to manually add the Modelfree4 results to the test. Anyway, I really hope I can get down to the bottom of this problem. Cheers, Edward