As described here: http://jenkins.361315.n4.nabble.com/Getting-NoSuchClassDefFoundError-for-ehcache-td391329.html, the spring-context-support JAR that is now (from version 1.502 on) packaged into the jenkins.war is loaded instead of the one from crowd/WEB-INF/lib. So it does not find classes from the ehcache JAR packaged only in the crowd/WEB-INF/lib.

(see attached jenkins.log for complete stack trace)

Two possible solutions:

1. remove the spring-context-support JAR from jenkins.war/WEB-INF/lib
2. switch class loader lookup order to search "plugin/WEB-INF/lib" first (this way it would be possible for plugin developers to override JARs delivered with the jenkins core)

This issue prevents me from using the newest jenkins versions (starting from 1.502).