I had trouble using the base Ubuntu 12.04 image on Amazon (ami-3d4ff254), so I've been making my own ami based on it that has Java and the build tools I need pre-installed. I have configured JClouds with "Use Pre-existing user" and "Use Pre-installed Java". The plug-in starts the machine, connects to it, then I get:

[#|2012-11-05T16:12:48.801-0500|WARNING|oracle-glassfish3.1.1|hudson.slaves.NodeProvisioner|_ThreadID=26;_ThreadName=Thread-2;|Provisioned slave testaws failed to launch
java.util.concurrent.ExecutionException: java.io.IOException: Error during SCP transfer.
at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
at java.util.concurrent.FutureTask.get(FutureTask.java:83)
at jenkins.plugins.jclouds.compute.JCloudsCloud$2.call(JCloudsCloud.java:227)
at jenkins.plugins.jclouds.compute.JCloudsCloud$2.call(JCloudsCloud.java:213)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.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:662)
Caused by: java.io.IOException: Error during SCP transfer.
at com.trilead.ssh2.SCPClient.put(SCPClient.java:510)
at com.trilead.ssh2.SCPClient.put(SCPClient.java:466)
at jenkins.plugins.jclouds.compute.JCloudsLauncher.launch(JCloudsLauncher.java:71)
at hudson.slaves.SlaveComputer$1.call(SlaveComputer.java:200)
... 5 more
Caused by: java.io.IOException: Remote scp sent illegal error code.
at com.trilead.ssh2.SCPClient.readResponse(SCPClient.java:53)
at com.trilead.ssh2.SCPClient.sendBytes(SCPClient.java:137)
at com.trilead.ssh2.SCPClient.put(SCPClient.java:506)
... 8 more

The failing line (JCloudsLauncher:71) appears to be trying to copy Slave.jar to /tmp on the node. I can manually scp this file and the manual scp succeeds. Any ideas on how to debug this?