[MMTK] Calculation of Molecular Surface

[mkseo]

Hi all,

I am trying to calculate molecular surface of protein.
I loaded PDB file, made protein object and calculate molecular surface 
using surfaceAndVolume() as follows:

universe.protein.surfaceAndVolume()

I got error "AttributeErro: 'Nontype' object has no attribute 
'srufaceAndvolume'
What is this about?

thanks