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.