Rabbitmq river

I'm trying to setup/configure a rabbitmq river (using es 0.16.2) and am
getting the following error in the logs:

[2011-07-06 09:53:38,883][DEBUG][river.cluster ] [Coldfire]
processing [reroute_rivers_node_changed]: execute
[2011-07-06 09:53:38,884][DEBUG][cluster.service ] [Coldfire]
processing [update-mapping [_river][optimizer_river]]: done applying updated
cluster_state
[2011-07-06 09:53:38,924][DEBUG][river.cluster ] [Coldfire]
cluster state updated, version [1], source [reroute_rivers_node_changed]
[2011-07-06 09:53:38,926][DEBUG][river.cluster ] [Coldfire]
processing [reroute_rivers_node_changed]: done applying updated
cluster_state
[2011-07-06 09:53:38,926][DEBUG][river ] [Coldfire]
creating river [rabbitmq][optimizer_river]
[2011-07-06 09:53:38,928][WARN ][river ] [Coldfire]
failed to create river [rabbitmq][optimizer_river]
org.elasticsearch.common.settings.NoClassSettingsException: Failed to load
class with value [rabbitmq]
at org.elasticsearch.river.RiverModule.loadTypeModule(RiverModule.java:84)
at org.elasticsearch.river.RiverModule.spawnModules(RiverModule.java:56)
at
org.elasticsearch.common.inject.ModulesBuilder.add(ModulesBuilder.java:44)
at org.elasticsearch.river.RiversService.createRiver(RiversService.java:127)
at
org.elasticsearch.river.RiversService$ApplyRivers$1.onResponse(RiversService.java:225)
at
org.elasticsearch.river.RiversService$ApplyRivers$1.onResponse(RiversService.java:220)
at
org.elasticsearch.action.support.single.shard.TransportShardSingleOperationAction$AsyncSingleAction$1.run(TransportShardSingleOperationAction.java:138)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:680)
Caused by: java.lang.ClassNotFoundException: rabbitmq
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at org.elasticsearch.river.RiverModule.loadTypeModule(RiverModule.java:70)
... 9 more

Here's my create request:

#create river:
curl -XPUT 'localhost:9200/_river/optimizer_river/_meta' -d '{
"type" : "rabbitmq",
"host":"127.0.0.1",
"user":"es_writer",
"password":"foo",
"vhost":"/elasticsearch",
"queue":"es_index",
"exchange":"es",
"routing_key":"es.optimizer.index"
}'

Any ideas on what I'm doing incorrectly?