vitero: issue with unexpected response element

15:03:23,229 ERROR ViteroManager:175 - Cannot remove an user from a group
-> Unexpected element {http://www.vitero.de/schema/group}successResponse found.   Expected {http://www.vitero.de/schema/group}removeUserFromGroupResponse.
-> Unexpected element {http://www.vitero.de/schema/group}successResponse found.   Expected {http://www.vitero.de/schema/group}removeUserFromGroupResponse.
>>>stack of 1.cause::javax.xml.ws.soap.SOAPFaultException: Unexpected element {http://www.vitero.de/schema/group}successResponse found.   Expected {http://www.vitero.de/schema/group}removeUserFromGroupResponse.
-> at org.apache.cxf.jaxws.JaxWsClientProxy.mapException(JaxWsClientProxy.java:195)
   at org.apache.cxf.jaxws.JaxWsClientProxy.invoke(JaxWsClientProxy.java:145)
   at com.sun.proxy.$Proxy131.removeUserFromGroup(Unknown Source)
   at org.olat.modules.vitero.manager.ViteroManager.removeFromRoom(ViteroManager.java:982)
   at org.olat.modules.vitero.manager.ViteroManager.removeFromRoom(ViteroManager.java:973)
   at org.olat.modules.vitero.ui.ViteroUserToGroupController.signOut(ViteroUserToGroupController.java:229)
   at org.olat.modules.vitero.ui.ViteroUserToGroupController.event(ViteroUserToGroupController.java:182)
   at org.olat.core.gui.control.DefaultController$1.run(DefaultController.java:250)
   at org.olat.core.logging.activity.ThreadLocalUserActivityLoggerInstaller.runWithUserActivityLogger(ThreadLocalUserActivityLoggerInstaller.java:108)
   at org.olat.core.gui.control.DefaultController.dispatchEvent(DefaultController.java:247)
   at org.olat.core.gui.control.DefaultController.fireEvent(DefaultController.java:194)
>>>stack of 2.cause::org.apache.cxf.interceptor.Fault: Unexpected element {http://www.vitero.de/schema/group}successResponse found.   Expected {http://www.vitero.de/schema/group}removeUserFromGroupResponse.
-> at org.apache.cxf.wsdl.interceptors.DocLiteralInInterceptor.validatePart(DocLiteralInInterceptor.java:281)
   at org.apache.cxf.wsdl.interceptors.DocLiteralInInterceptor.handleMessage(DocLiteralInInterceptor.java:191)
   at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:308)
   at org.apache.cxf.endpoint.ClientImpl.onMessage(ClientImpl.java:826)
   at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.handleResponseInternal(HTTPConduit.java:1695)
   at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.handleResponse(HTTPConduit.java:1572)
   at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.close(HTTPConduit.java:1373)
   at org.apache.cxf.transport.AbstractConduit.close(AbstractConduit.java:56)
   at org.apache.cxf.transport.http.HTTPConduit.close(HTTPConduit.java:673)
   at org.apache.cxf.interceptor.MessageSenderInterceptor$MessageSenderEndingInterceptor.handleMessage(MessageSenderInterceptor.java:63)
   at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:308)