error file PreW2_ivf.exe

hi, I am trying to apply CE-QUAL for my reservoir. When I run PreW2_ivf.exe,i got an error "input conversion error, unit 31, file graph.npt....". I checked the file graph.npt several times and I think the graph file is correct. But I still get this error when I run PreW2_ivf.exe. I would appreciate if you can help me soon. Thank you. Huyen