Error when trying to Preview a form

I get the following error (Bonita Studio Log) whenever I try to preview a form.

!ERROR The object 'org.bonitasoft.studio.model.process.impl.ActorImpl@7b495ebe (documentation: , name: Salgsavdelingen, initiator: true)' is not contained in a resource. !STACK 0 org.eclipse.emf.ecore.resource.Resource$IOWrappedException: The object 'org.bonitasoft.studio.model.process.impl.ActorImpl@7b495ebe (documentation: , name: Salgsavdelingen, initiator: true)' is not contained in a resource. at org.eclipse.emf.ecore.xmi.impl.XMLSaveImpl.endSave(XMLSaveImpl.java:301) at org.eclipse.emf.ecore.xmi.impl.XMLSaveImpl.save(XMLSaveImpl.java:265) at org.eclipse.emf.ecore.xmi.impl.XMLResourceImpl.doSave(XMLResourceImpl.java:365) at org.eclipse.emf.ecore.resource.impl.ResourceImpl.save(ResourceImpl.java:1430) at org.eclipse.emf.ecore.resource.impl.ResourceImpl.saveOnlyIfChangedWithMemoryBuffer(ResourceImpl.java:1144) at org.eclipse.emf.ecore.resource.impl.ResourceImpl.save(ResourceImpl.java:985) at org.bonitasoft.studio.form.preview.FormPreviewOperation.doCreateEMFResource(FormPreviewOperation.java:266) at org.bonitasoft.studio.form.preview.FormPreviewOperation.run(FormPreviewOperation.java:172) at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121)

I use: Bonita BPMCommunity-6.4.1-Tomcat-7.0.55

java version "1.7.0_71" Java(TM) SE Runtime Environment (build 1.7.0_71-b14) Java HotSpot(TM) 64-Bit Server VM (build 24.71-b01, mixed mode)

Operating System: Windows 8.1 64-bit

How do I solve this problem?