All the classloading issues you may have should be solved using the ReflexRunner class. This class runs your main class using the java agent mode (this is part of the JVM since Java 5) which avoids the use of custom classloaders (like the one used by Reflex in the past).
This kind of problem can be caused by many factors, but among the common ones you can find:
SomeClass.class.getName() new SomeClass()