Following this KB article, http://kb.flexerasoftware.com/selfse...rnalID=Q000043, it will walk you through the steps to diagnose the problem.
These types of problems are usually related to missing resources. Your class may not be found and still exist in the installer but if it's dependencies are not available then it cannot be loaded into the VM. This is misleading because it's the dependency that cannot be found. So go back and make sure that all of the required libraries are set as dependencies in the IDE.