RS: cannot delete a question in question bank

11:59:06,061 ERROR OLATRuntimeException:175 - OLAT::ERROR ^%^ N1-E25 ^%^ org.olat.core.logging 
https://xyz.de/auth/QPool/0/My/0 ^%^ Mozilla/5.0 (Windows NT 6.1; WOW64; rv:39.0) Gecko/20100101 Firefox/39.0
**RedScreen** Unable to find org.olat.basesecurity.SecurityGroupImpl with id 1553826105

<dispatchinfo>
	<componentinfo>
		<compname>ffo_main_delete_confirmation</compname>
		<compclass>org.olat.core.gui.components.form.flexible.impl.FormWrapperContainer</compclass>
		<extendedinfo>n/a</extendedinfo>
		<event>
			<class&gt;org.olat.core.gui.control.Event</class&gt;
			<command>validation ok</command>
			<tostring>com:validation ok,org.olat.core.gui.control.Event@d62b3f02</tostring>
		</event>
	</componentinfo>
	<controllerinfo>
		<controllername>org.olat.modules.qpool.ui.DeleteConfirmationController</controllername>
		<controllername>org.olat.modules.qpool.ui.QuestionListController</controllername>
		<controllername>org.olat.modules.qpool.ui.QuestionPoolMainEditorController</controllername>
		<controllername>org.olat.core.commons.fullWebApp.BaseFullWebappController</controllername>
	</controllerinfo>
</dispatchinfo>

>>> stack of 1.cause::org.olat.core.logging.OLATRuntimeException: Unable to find org.olat.basesecurity.SecurityGroupImpl with id 1553826105
-> at org.olat.core.gui.exception.ExceptionWindowController.<init>(ExceptionWindowController.java:116)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:57)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:46)
   at org.olat.core.gui.components.Window.dispatchRequest(Window.java:589)
   at org.olat.core.gui.components.Window.doDispatchRequest(Window.java:282)
   at org.olat.core.gui.components.AbstractComponent.dispatchRequest(AbstractComponent.java:193)
   at org.olat.dispatcher.AuthenticatedDispatcher.processValidDispatchURI(AuthenticatedDispatcher.java:273)
   at org.olat.dispatcher.AuthenticatedDispatcher.execute(AuthenticatedDispatcher.java:190)
   at org.olat.core.servlets.OpenOLATServlet.executeUserRequest(OpenOLATServlet.java:289)
   at org.olat.core.servlets.OpenOLATServlet.doPost(OpenOLATServlet.java:232)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:644)
>>> stack of 2.cause::javax.persistence.EntityNotFoundException: Unable to find org.olat.basesecurity.SecurityGroupImpl with id 1553826105
-> at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$JpaEntityNotFoundDelegate.handleEntityNotFound(EntityManagerFactoryBuilderImpl.java:158)
   at org.hibernate.event.internal.DefaultLoadEventListener.load(DefaultLoadEventListener.java:227)
   at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:262)
   at org.hibernate.event.internal.DefaultLoadEventListener.doOnLoad(DefaultLoadEventListener.java:121)
   at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:89)
   at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1239)
   at org.hibernate.internal.SessionImpl.access$1900(SessionImpl.java:203)
   at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.doGetReference(SessionImpl.java:2749)
   at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.getReference(SessionImpl.java:2728)
   at org.hibernate.internal.SessionImpl.getReference(SessionImpl.java:3476)
   at org.olat.basesecurity.BaseSecurityManager.deleteSecurityGroup(BaseSecurityManager.java:546)