Generate Hibernate/JPA seem to cause slow down and excessive look ups

I don't get this so often, but when I double click entities I gives me this error often:

Java Model Exception: Java Model Status [hibernatetools.doc does not exist]
at org.eclipse.jdt.internal.core.JavaElement.newJavaModelException(JavaElement.java:501)
at org.eclipse.jdt.internal.core.Openable.generateInfos(Openable.java:245)
at org.eclipse.jdt.internal.core.JavaElement.openWhenClosed(JavaElement.java:514)
at org.eclipse.jdt.internal.core.JavaElement.getElementInfo(JavaElement.java:251)
at org.eclipse.jdt.internal.core.JavaElement.getElementInfo(JavaElement.java:237)
at org.eclipse.jdt.internal.core.JavaProject.getJavaProjectElementInfo(JavaProject.java:1497)
at org.eclipse.jdt.internal.core.JavaProject.newNameLookup(JavaProject.java:2197)
at org.eclipse.jdt.internal.core.JavaProject.newNameLookup(JavaProject.java:2207)
at org.eclipse.jdt.internal.core.JavaProject.findType(JavaProject.java:1230)
at org.eclipse.jdt.internal.core.JavaProject.findType(JavaProject.java:1137)
at org.hibernate.eclipse.jdt.ui.internal.jpa.common.Utils.findCompilationUnit(Utils.java:68)
at org.hibernate.eclipse.jdt.ui.internal.jpa.actions.JPAMapToolActor.updateSelectedItems(JPAMapToolActor.java:201)
at org.hibernate.eclipse.jdt.ui.internal.jpa.actions.JPAMapToolActionDelegate.selectionChanged(JPAMapToolActionDelegate.java:45)
at org.eclipse.ui.internal.PluginAction.refreshEnablement(PluginAction.java:206)
at org.eclipse.ui.internal.PluginAction.createDelegate(PluginAction.java:126)
at org.eclipse.ui.internal.PluginAction.selectionChanged(PluginAction.java:275)
at org.eclipse.ui.internal.PluginAction.selectionChanged(PluginAction.java:289)
at org.eclipse.ui.internal.ViewerActionBuilder$ViewerContribution.selectionChanged(ViewerActionBuilder.java:191)
at org.eclipse.jface.viewers.Viewer$2.run(Viewer.java:162)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37)
at org.eclipse.core.runtime.Platform.run(Platform.java:880)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:48)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
at org.eclipse.jface.viewers.Viewer.fireSelectionChanged(Viewer.java:160)
at org.eclipse.jface.text.TextViewer.fireSelectionChanged(TextViewer.java:2558)
at org.eclipse.jface.text.TextViewer.selectionChanged(TextViewer.java:2541)
at org.eclipse.jface.text.TextViewer.setSelectedRange(TextViewer.java:2320)
at org.eclipse.jface.text.TextViewer$ViewerState.restore(TextViewer.java:1189)
at org.eclipse.jface.text.TextViewer.enabledRedrawing(TextViewer.java:4721)
at org.eclipse.jface.text.TextViewer.enabledRedrawing(TextViewer.java:4696)
at org.eclipse.jface.text.TextViewer.setRedraw(TextViewer.java:4783)
at org.eclipse.jface.text.TextViewer.setRedraw(TextViewer.java:4755)
at org.eclipse.jface.text.TextViewer$RewriteTarget.setRedraw(TextViewer.java:1051)
at org.eclipse.jface.text.TextViewer$DocumentRewriteSessionListener.documentRewriteSessionChanged(TextViewer.java:1419)
at org.eclipse.jface.text.AbstractDocument.fireRewriteSessionChanged(AbstractDocument.java:1516)
at org.eclipse.jface.text.AbstractDocument.stopRewriteSession(AbstractDocument.java:1602)
at org.eclipse.ltk.core.refactoring.TextChange.perform(TextChange.java:256)
at org.eclipse.ltk.core.refactoring.CompositeChange.perform(CompositeChange.java:278)
at org.eclipse.ltk.core.refactoring.CompositeChange.perform(CompositeChange.java:278)
at org.eclipse.ltk.core.refactoring.PerformChangeOperation$1.run(PerformChangeOperation.java:260)
at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1800)
at org.eclipse.ltk.core.refactoring.PerformChangeOperation.executeChange(PerformChangeOperation.java:308)
at org.eclipse.ltk.internal.ui.refactoring.UIPerformChangeOperation.access$1(UIPerformChangeOperation.java:1)
at org.eclipse.ltk.internal.ui.refactoring.UIPerformChangeOperation$1.run(UIPerformChangeOperation.java:66)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37)
at org.eclipse.ltk.internal.ui.refactoring.UIPerformChangeOperation$2.run(UIPerformChangeOperation.java:84)
at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:133)
at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3800)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3425)
at org.eclipse.jface.operation.ModalContext$ModalContextThread.block(ModalContext.java:172)
at org.eclipse.jface.operation.ModalContext.run(ModalContext.java:370)
at org.eclipse.ltk.internal.ui.refactoring.RefactoringWizardDialog2.run(RefactoringWizardDialog2.java:317)
at org.eclipse.ltk.ui.refactoring.RefactoringWizard.internalPerformFinish(RefactoringWizard.java:558)
at org.eclipse.ltk.ui.refactoring.UserInputWizardPage.performFinish(UserInputWizardPage.java:154)
at org.eclipse.ltk.ui.refactoring.RefactoringWizard.performFinish(RefactoringWizard.java:622)
at org.eclipse.ltk.internal.ui.refactoring.RefactoringWizardDialog2.okPressed(RefactoringWizardDialog2.java:446)
at org.eclipse.jface.dialogs.Dialog.buttonPressed(Dialog.java:472)
at org.eclipse.jface.dialogs.Dialog$2.widgetSelected(Dialog.java:624)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:228)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3823)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3422)
at org.eclipse.jface.window.Window.runEventLoop(Window.java:825)
at org.eclipse.jface.window.Window.open(Window.java:801)
at org.eclipse.ltk.ui.refactoring.RefactoringWizardOpenOperation$1.run(RefactoringWizardOpenOperation.java:144)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ltk.ui.refactoring.RefactoringWizardOpenOperation.run(RefactoringWizardOpenOperation.java:156)
at org.eclipse.jdt.internal.ui.refactoring.actions.RefactoringStarter.activate(RefactoringStarter.java:37)
at org.hibernate.eclipse.jdt.ui.internal.jpa.process.AllEntitiesProcessor.showRefactoringDialog(AllEntitiesProcessor.java:360)
at org.hibernate.eclipse.jdt.ui.internal.jpa.process.AllEntitiesProcessor.modify(AllEntitiesProcessor.java:167)
at org.hibernate.eclipse.jdt.ui.internal.jpa.actions.JPAMapToolActor.updateSelected(JPAMapToolActor.java:118)
at org.hibernate.eclipse.jdt.ui.internal.jpa.actions.JPAMapToolActionPulldownDelegate.runWithEvent(JPAMapToolActionPulldownDelegate.java:150)
at org.eclipse.ui.internal.PluginAction.runWithEvent(PluginAction.java:241)
at org.eclipse.ui.internal.WWinPluginAction.runWithEvent(WWinPluginAction.java:229)
at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:583)
at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:500)
at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:411)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3823)