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Problem when invoking code from plug-in: org.eclipse.core.resources

Question asked by jacobvos on May 1, 2014
First: I am a business process designer, not that technical, and investigating possibilities of Activiti Designer. I have an issue that is maybe very simple to solve and everyone with some more technical knowledge than I have, would have solved it. So on beforehand: my apologize!

- installed Eclipse Juno;
- installed the Activiti Designer software on it;
- installed Maven;
- created a new project of the kind 'Activiti';
- configured the project as a Maven one;
- added Activiti libraries (from two sources) to the Java Build Path;
- added library JUnit 4;
- imported the 'bpmn-examples', by which at least the pom.xml file is overwritten;
- updated the project ('Maven > Update Project…').

Then I want to proceed with 'Say hello to Activiti' like is written in the book 'Activiti in Action'. But…

When I want to 'Run as Test > JUnit Test' the file '' (from which I removed "chapter1/") I get the error: "Errors exist in required project(s): <myProjectName>".

I have already errors before trying to perform that action:
"Problems occurred when invoking code from plug-in: "org.eclipse.core.resources".

java.lang.ClassCastException: org.eclipse.core.internal.resources.WorkspaceRoot cannot be cast to org.eclipse.core.resources.IProject
   at org.activiti.designer.eclipse.navigator.project.ProjectTreeContentProvider.visit(
   at org.activiti.designer.eclipse.navigator.AbstractTreeContentProvider.resourceChanged(
   at org.eclipse.core.internal.resources.Workspace.broadcastPostChange(
   at org.eclipse.core.internal.resources.Workspace.endOperation(
   at org.eclipse.debug.core.model.LaunchConfigurationDelegate.buildProjects(
   at org.eclipse.debug.core.model.LaunchConfigurationDelegate.buildForLaunch(
   at org.eclipse.debug.internal.core.LaunchConfiguration.launch(
   at org.eclipse.debug.internal.core.LaunchConfiguration.launch(
   at org.eclipse.debug.internal.ui.DebugUIPlugin.buildAndLaunch(
   at org.eclipse.debug.internal.ui.DebugUIPlugin$

If somebody can help me, that would be nice!

Kind regards,
Jacob Vos