1373176 - KM Business Objects Enterprise 3.1 SP2 with SAP portal Integration fails with network error

When trying to acces a Business Objects KM repository through an SAP Enterprise Portal the following error appears

• Your operation cannot be fulfilled due to a network problem, please try again.

extract from EP Default-trace log

•  #1.5#005056B44D60005F0000043D000015B800047061D857C6E1#1249465451105#com.businessobjects.kmc.manager.BOERepositoryManager#sap.com/irj#com.businessobjects.kmc.manager.BOERepositoryManager#marinawalden#43724##n/a##60b5f25081a411deace2005056b44d60#SAPEngine_Application_Thread[impl:3]_35##0#0#Error##Plain###remote login failed: (407)Proxy Authentication Required#

  #1.5#005056B44D60005F0000043E000015B800047061D857E2A7#1249465451120#com.sapportals.wcm.WcmException#sap.com/irj#com.sapportals.wcm.WcmException.WcmException(90)#testuser#43724##n/a##60b5f25081a411deace2005056b44d60#SAPEngine_Application_Thread[impl:3]_35##0#0#Error##Plain###Your operation cannot be fulfilled due to a network problem, please try again. com.sap.netweaver.bc.rf.common.exception.ResourceException: Your operation cannot be fulfilled due to a network problem, please try again.

  at com.businessobjects.kmc.manager.BOEConnector.processRemoteException(Unknown Source)
  at com.businessobjects.kmc.manager.BOEConnector.processRemoteException(Unknown Source)
  at com.businessobjects.kmc.manager.BOEConnector.initLogon(Unknown Source)
  at com.businessobjects.kmc.manager.BOEConnector.login(Unknown Source)
  at com.businessobjects.kmc.manager.BOERepositoryManager.initUserSession(Unknown Source)
  at com.businessobjects.kmc.manager.BOENamespaceManager.findResources(Unknown Source)
  at com.sapportals.wcm.repository.CollectionImpl2.internalGetChildrenManager(CollectionImpl2.java:310)
  at com.sapportals.wcm.repository.CollectionImpl.internalGetChildren(CollectionImpl.java:1621)

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