I have some class loading problems with the Ical module. In it's scheduled event (which is sending the ICal invites) it goes wrong on line 216 where it executes this: DateTime start = new DateTime( this.StartDateTime ), end = new DateTime( this.EndDateTime ); Note that this DateTime is coming from one of the imported Jars of ical4j Right on this line (when debugging) the whole application crashes with this error in the Mendix log java.lang.NoClassDefFoundError: edu/emory/mathcs/backport/java/util/concurrent/ConcurrentHashMap And this error in the eclipse console log SLF4J: Failed to load class "org.slf4j.impl.StaticMDCBinder". SLF4J: Defaulting to no-operation MDCAdapter implementation. SLF4J: See http://www.slf4j.org/codes.html#no_static_mdc_binder for further details. From the website of SLF4J This error indicates that appropriate SLF4J binding could not be found on the class path. Placing one (and only one) of slf4j-nop.jar, slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar or logback-classic.jar on the class path should solve the problem. I tried adding jars containing these classes in the userlib but it seems to conflict with the logging.jar which is in the program files/Mendix/5.9.0/runtime/bundles directory. Really hoping that someone can help me out here..