The jserv.log and OACoreGroup..stderr (where is the number of the JVM) will show errors like:-
Exception in static block of jtf.cache.CacheManager. Stack trace is: oracle.apps.jtf.base.resources.FrameworkException: IAS Cache initialization failed. The Distributed Caching System failed to initialize on port: 12346. The list of hosts in the distributed caching system is: hostA.domain.com . The port 12346 should be free on each host running the JVMs. The default port 12346 can be overridden using -Doracle.apps.jtf.cache.IASCacheProvidercacheProvider.port= at oracle.apps.jtf.cache.IASCacheProvider.init(IASCacheProvider.java:220) at oracle.apps.jtf.cache.CacheManager.activateCache(CacheManager.java:1444) at oracle.apps.jtf.cache.CacheManager.initCache(CacheManager.java:752)
java.lang.NoClassDefFoundError at org.apache.jserv.JServServletManager.load_init(JServServletManager.java:765) at org.apache.jserv.JServServletManager.loadServlet(JServServletManager.java:659
SOLUTION
Disable Java Caching Mechanism.
Comment out the following line in jserv.propertiesto disable Java Caching