Hi Elaine, Hope you are fine. If you remember I was calculating per residue SASA using Chimera for my MD simulated protein. At that time it was working fine. But I did some more simulation run and now I want to calculate SASA for the entire trajectory but unfortunately Its showing the following error. *Error* Problem in per-frame script: IOError: [Errno 13] Permission denied: 'sas111.txt' File "<string>", line 3, in <module> See reply log for Python traceback. For your reference, I am giving the script also. It was working fine previously but with the same procedure which I followed this script is not working and showing the above mentioned error. * Script * from chimera import openModels, Molecule out = open("sas111.txt", "a") x='---------------------------------------------------------------------------------' for m in openModels.list(modelTypes=[Molecule]): for r in m.residues: try: sas = r.areaSAS except AttributeError: continue print>>out, r, sas print>>out,x out.close() Kindly help me. Thank you. Aditya.