Hi forum members, I’ve just completed the Crash Course learning path, but have one exercise that I can’t get functioning correctly at runtime in section 12 – Extending Your Business Logic. This exercise uses OptaPlanner to build out a scheduling function in Java. Writing Your First Java Action Everything compiles okay, I had to set the JDK Compliance to 11 and JRE to version 11 in Eclipse for the build to run from Studio Pro. I get the following error at runtime when the microflow calls the planner action. java.lang.IncompatibleClassChangeError: Method org.optaplanner.core.api.solver.SolverFactory.create(Lorg/optaplanner/core/config/solver/SolverConfig;)Lorg/optaplanner/core/api/solver/SolverFactory; must be InterfaceMethodref constant at usermanager.actions.Planner.executeAction(Planner.java:59) I’ve used both the build out from the exercise notes and the sample files provided in the Java archive provided, but I get the same error with both. I’ve looked through the Optaplanner examples and the call flow looks correct, this is the call flow snippet within Planner.Java // BEGIN USER CODE String SOLVER_CONFIG_XML = "solver.xml"; SolverConfig solverConfig = SolverConfig.createFromXmlResource(SOLVER_CONFIG_XML); SolverFactory<ShiftSolution> solverFactory = SolverFactory.create(solverConfig); ← Runtime error here Solver<ShiftSolution> solver = solverFactory.buildSolver(); ShiftSolution shiftSolution = new ShiftSolution(); I’ve tried using both the latest 8.0.0 and 7.3.3 versions of OptaPlanner which the course notes were derived from, but still get the same error. I understand the theory of the Java API and what’s been built out in the exercise, but it would be good to understand how to fix this error so I can test the scheduling function in the built out app. If there are any forum members who’ve recently been through the same training and can provide any guidance that would great.