CommGen successful in online preview, but not when running

We have just set up a new email communication for financial aid,

and have tested it (successfully) multiple times with online

preview, but when we run it for real, we get a "missing critical

data" error (Unable to derive Address for Person

Communication Usage).  We are using the same address usage for

other email communications.  The students I have checked all

have the campus email address (first in the address usage

sequence).  I also substituted a student's campus email

address with my campus address, and still got the "missing critical

data" error.   The print version of this same communication runs fine.