I only see failure when I'm trying to remote deploy to a JBoss 4.2.3 GA instance. I've ensured the servers can speak to each other, and I've manually placed a war on the deploying server's normal (port 80) webserver and manually crafted the URL the Cargo makes to hit it, and that works fine, too. So all connectivity seems fine.
The only things that seems to me to be wrong is that the filename in the URL in the example at http://cargo.codehaus.org/JBoss+Remote+Deployer#JBossRemoteDeployer-JBoss40xand42x contains "-1.0-SNAPSHOT" and even though I am trying to deploy a snapshot, too, I only have "fly-garmin.war" with no version or "-SHAPSHOT".
Here is what I have in my POM...