[lammps-users] fix msd

I think your fix command is the problem. The manual site:
says that it'll take the optional keyword, com, but the pdf manual has no
mention of it. Also, looking at the source itself (for the latest
version), it'll only take exactly 5 arguments. So, maybe the online
documentation is out of date?

Jon Brown

The on-line doc pages are always for the most current
(fully patched) version. Fix msd com was added receently
as a patch.