We have started to get an error saying that the Slave Agent cannot be launched due to our security settings. There appear to be some workarounds, however, the recommended solution is to ensure that the JNLPs are properly signed. See

http://www.java.com/en/download/help/java_blocked.xml

for some context

And

http://jenkins-ci.361315.n4.nabble.com/Java-Version-7-Update-45-warning-every-time-I-try-starting-the-slave-td4679570.html

for a discussion around the issues.