7.3 Schedulertask shows NoClassDefFoundError : UserManagementException

HI,

i need some help with my first scheduler task in the 7.3 Netweaver :

I am trying to get a XML Document stored in KM

    public Vector<String> initializeUserData(String exceptionList){

  IResourceFactory resurceFactory = null;

  IResource resourceUser = null;

  Document userDoc = null;

  Vector<String> users = new Vector<String>();

  try {

  IServiceUserFactory userfact=UMFactory.getServiceUserFactory();

  IUser tempUser = userfact.getServiceUser("cmadmin_service");

  IResourceContext ctxt = ResourceContext.getInstance(tempUser);

  if (logger.beDebug())

  logger.debugT("initializeData ctxt: " + ctxt);

  RID userNotToChange = RID.getRID(exceptionList);

  resurceFactory = ResourceFactory.getInstance();

  if (logger.beDebug()){

  logger.debugT("initializeData resurceFactory: " + resurceFactory);

  }

  resourceUser  = resurceFactory.getResource(userNotToChange, ctxt);

  userDoc  = parseXML(resourceUser.getContent().getInputStream());

  users = fillUserList(userDoc);

  } catch (ResourceException e) {

  logger.errorT("ResourceException initializeData: " + getStackTrace(e));

  } catch (Exception ex) {

  logger.errorT("Exception initializeData: " + getStackTrace(ex));

  }

  return users;

  }

The result is the following Exception:

avax.ejb.EJBException: nested exception is: java.lang.RuntimeException: java.lang.NoClassDefFoundError: com/sapportals/portal/security/usermanagement/UserManagementException

java.lang.RuntimeException: java.lang.NoClassDefFoundError: com/sapportals/portal/security/usermanagement/UserManagementException

which points to the following line :

IResourceContext ctxt = ResourceContext.getInstance(tempUser);

I have referenced the JAR in the build path:

tc~je~usermanagement~api.jar

Any ideas ?