In REST API version 1.0 (running a LiveCD on VirtualBox), I got the following error message when I tried to install a jenkins-client on my application.

Could not embed cartridges for application test2
Could not request https://192.168.56.101/broker/rest/domains/devoxx/applications/test2/cartridges: Operation failed on parameter "cartridge", sevirty "ERROR" with exit code "157".Reason given: "Error contacting Jenkins server.
Could not download https://jenkins-devoxx.example.com/jnlpJars/jenkins-cli.jar"

I also created the jenkins application since I did not have one in my domain before, so my guess is that the lib download occurred before the application was available, which ended up with that error message.

Trying to install the same jenkins-client embedded cartridge a few minutes later worked.