Procmail error: invalid shell for mailing to programs?

I'm trying to call procmail from .forward.  The contents of .forward
are:

"|exec /usr/bin/procmail #user"

The error message back is:
    User MyUser(_at_)mycompany(_dot_)com doesn't have a valid shell for mailing 
to
programs

Any idea what this means and how to fix it?  Pls send replies to
alweiner(_at_)earth(_dot_)presstar(_dot_)com(_dot_)  Thanx!