This is still a weird string/unicode error I think, where it's saying that something is None when it's not. I'll look at this tomorrow.
$ openmm --coords input.pdb --protein amber99sb --water tip3p | tee openmm.out
[OpenMM] ERROR | The 'protein' trait of the general section instance must be any of ['amber96', 'amber99sb', 'amber99sb-ildn', 'amber99sb-nmr', 'amber03', 'amber10', 'amoeba2009'] or None, but a value of 'None' <type 'str'> was specified.
To see all available configurables, use `--help-all`
This is still a weird string/unicode error I think, where it's saying that something is None when it's not. I'll look at this tomorrow.