cannot set dns maximum-length

I am trying to change my dns maximum-length to something high.

Everytime I try to do I get:

ERROR: % Invalid input detected at '^' marker.

Here is the steps I am taking to set it up. (this is from the 7.x command line interface guide)

hostname(config)# class-map dns-port hostname(config-cmap)# match port udp eq 53 hostname(config-cmap)# exit hostname(config)# policy-map sample_policy hostname(config-pmap)# class dns-port hostname(config-pmap-c)# inspect dns maximum-length 1500

Except when i get to the above line, I get this message:

ERROR: % Invalid input detected at '^' marker.

My instructions are straight out of the Cisco CLI refernece guide.

Any ideas why? Am I forgetting a step somewhere?

My hardware is a ASA 5510.

If you need my running-config, please reply and I will post it.

Thanks!