[gmx-users] Problems with using AFM Pulling

[Bob Johnson]

Hello everyone,
I'm trying to use the AFM pulling feature in Gromacs. However, every time I run
mdrun I get the following error:

Groups: 5P
Pull code using absolute reference.
Using 1 pull groups
Using distance components 0 0 1

Back Off! I just backed up pull.pdo to ./#pull.pdo.1#
Fatal error: Can't find group  in the index file

In my index file I have the following:

[ 5P ]
  32

Along with additional groups not used in the pull. I don't understand why mdrun
can't find the 5P group that I defined. Does anyone know what's wrong?
Thanks,
Bob Johnson