Lalit, I think it's because your restraints are specifying segid A while your CNS files specify an empty string for the segid. Probably the simplest solution is to tell CNS/XPLOR-NIH to generate your molecule with the segid set. Dr. Brian O. Smith ---------------------- B Smith at bio gla ac uk Division of Molecular & Cellular Biology, Faculty of Biomedical & Life Sciences, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, UK. Tel: 0141 330 5167/6459/3089 Fax: 0141 330 4600 ------------------------------------------------------------------- The University of Glasgow, charity number SC004401