I recently got also the classNotFoundExceptions. I resolved that with downloading and adding slf4j-api-1.7.22.jar, slf4j-log4j12-1.7.22.jar and slf4j-jdk14-1.7.22.jar to the userlib dir. Hope that helps.
Thanks for your suggestion. Sadly I am know getting a new error:
java.lang.ExceptionInInitializerError: null
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at io.netty.util.internal.logging.InternalLoggerFactory.<clinit>(InternalLoggerFactory.java:44)
Caused by: java.security.AccessControlException: access denied ("java.util.PropertyPermission" "io.netty.initialSeedUniquifier" "read")
This is probably due to the emulate cloud settings.