Hi @prangley,
Thanks for reporting this. The error indicates that the number of particles in the actual .mrc particle stack file on disk are not the same as cryoSPARC expects given the metadata files (.cs files).
Usually something like this happens when people try to import particles from another program and have given the wrong pair of .star and .mrc files, but that is obviously not the case here.
Can you check to see if the number of particles reportedly outputted by the template picker job matches the number reportedly read in by the 2D class job? (in the streamlog of the 2D class, before the error, you should see a line that says Loading a ParticleStack with XXX items)