[gmx-users] mdrun: In option s, required option was not provided and the default file 'topol' does not exist or not accessible

[Mohammed I Sorour]

Dear Gromacs users,

I'm running MD simulation on a couple of DNA systems that only vary in
sequence. Most of the runs worked just fine, but surprisingly I have one
system that I got an error in the NVT equilibration step.
I'm following the tutorial
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin/gmx-tutorials/lysozyme/06_equil.html

rogram:     gmx mdrun, version 2016.3
Source file: src/gromacs/options/options.cpp (line 258)
Function:    void gmx::Options::finish()

Error in user input:
Invalid input values
  In option s
    Required option was not provided, and the default file 'topol' does not
    exist or is not accessible.
    The following extensions were tried to complete the file name:
      .tpr

I'm pretty sure that I have the .tpr  files in the local directory. I have
read the previous reviews of the Gromacs mailing list, but I