Using CIDR and md5 in pg_hba.conf

Hello all;

I am trying to connect to a postgreSQL server running version 7.3.2 on
freebsd (5.1). I'm having trouble getting the syntax right for this
subnet. I thought I had this working at home for a simple
192.168.0.0/24 network. This is the line in the pg_hba.conf

host all all 10.16.0.0/12 trust

I restarted the server each time I make a change to the file but get
error "missing or erroneous pg_hba.conf file"

I can connect fine as long as I put only my IP and netmask in. I went
on the internet to make sure I have the right subnet and CIDR, so I
think it's correct. My server at home is running an older version
(7.1.?3) so perhaps something has changed, but I can't help but think
that I'm having a brain cramp here. Any hints would be most welcome.

Cheryl Bender