2199240 - Portal service hook could not be started

Search for the application "com.sap.portal.runtime.system.hooks" in nwa and on starting the hook service, an error is thrown "Portal service hook could not be started". On anlyzing the traces following error coould be seen :

Error: [PortalAppBroker.getPortalService() failed com.sap.portal.runtime.system.hooks|hook
[EXCEPTION]
com.sap.portal.prt.om.ObjectNotAvailableException: Object: [com.sap.portal.runtime.system.hooks|hook] load failed
    at com.sap.portal.prt.om.ObjectsManager.createObejctHandle(ObjectsManager.java:246)
    at com.sap.portal.prt.om.ObjectsManager.getObjectHandle(ObjectsManager.java:147)

(…)

Caused by: com.sap.portal.prt.broker.PortalServiceInstantiationException: Could not instantiate implementation class com.sapportals.portal.prt.service.hook.HookService of Portal Service com.sap.portal.runtime.system.hooks|hook because: Error occured during the instansiation process. Check the cause exception for more details.
    at com.sap.portal.prt.broker.PortalServiceItem.createServiceInstance(PortalServiceItem.java:310)

(…)

Caused by: java.lang.ClassNotFoundException: com.sapportals.portal.prt.service.hook.HookService
------------------------- Loader Info -------------------------
ClassLoader name: [WCE_PRIVATE_CL_sap.com/com.sap.portal.runtime.system.hooks]
Loader hash code: <no.>
Living status: alive
Direct parent loaders:
[sap.com/com.sap.portal.runtime.system.hooks]
Resources:
/usr/sap/<SID>/<Instance no.>/j2ee/cluster/apps/sap.com/com.sap.portal.runtime.system.hooks/servlet_jsp/com.sap.portal.runtime.system.hooks/root/WEB-INF/private/lib/com.sap.portal.runtime.system.hooks_core.jar
/usr/sap/<SID>/<Instance no.>/j2ee/cluster/apps/sap.com/com.sap.portal.runtime.system.hooks/servlet_jsp/com.sap.portal.runtime.system.hooks/work
/usr/sap/<SID>/<Instance no.>/j2ee/cluster/apps/sap.com/com.sap.portal.runtime.system.hooks/servlet_jsp/com.sap.portal.runtime.system.hooks/root/WEB-INF/private/classes
---------------------------------------------------------------
    at com.sap.engine.boot.loader.MultiParentClassLoader.loadClass(MultiParentClassLoader.java:280)

"Image/data in this KBA is from SAP internal systems, sample data, or demo systems. Any resemblance to real data is purely coincidental."

• SAP NetWeaver 7.3
• SAP enhancement package 1 for SAP NetWeaver 7.3
• SAP NetWeaver 7.4
• SAP NetWeaver 7.5

Enterprise Portal 7.30, EP 7.30, Enterprise Portal 7.31, EP 7.31, Enterprise Portal 7.40, EP 7.4,Enterprise Portal 7.50, EP 7.5 /nwa, java application, service, hook, class loader, com.sapportals.portal.prt.service.hook.HookService, com.sap.portal.runtime.system.hooks_core.jar, com.sap.portal.prt.broker.PortalServiceItem.createServiceInstance, com.sap.portal.runtime.system.hooks , KBA , EP-PIN-PRT , Portal Runtime , Problem