Application Mapping

I am trying to categorize our http traffic using Application mapping, I've done the following

80 TCP 10.0.0.0 Netmask: 255.0.0.0 http_VAC-Internal
80 TCP 167.74.0.0 Netmask: 255.255.0.0 http_BlueCross
80 TCP All http

unfortunately 80 TCP 10.0.0.0 Netmask: 255.0.0.0 Vac-internal-http does not seem to work but 80 TCP 167.74.0.0 Netmask: 255.255.0.0 http_BlueCross does.