Error during Enterprise Portal startup

Hi

While trying to access my Enterprise portal installation the screen throws the following stack trace. Can someone quickly respond with a solution. This portal installation has been running fine for the past two years now

Application error occurs during processing the request.

Details: java.lang.NullPointerException

at com.sap.portal.navigation.Gateway.service(Gateway.java:74)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)

at com.sap.engine.services.servlets_jsp.server.HttpHandlerImpl.runServlet(HttpHandlerImpl.java:385)

at com.sap.engine.services.servlets_jsp.server.HttpHandlerImpl.handleRequest(HttpHandlerImpl.java:263)

at com.sap.engine.services.httpserver.server.RequestAnalizer.startServlet(RequestAnalizer.java:340)

at com.sap.engine.services.httpserver.server.RequestAnalizer.startServlet(RequestAnalizer.java:318)

at com.sap.engine.services.httpserver.server.RequestAnalizer.invokeWebContainer(RequestAnalizer.java:821)

at com.sap.engine.services.httpserver.server.RequestAnalizer.handle(RequestAnalizer.java:239)

at com.sap.engine.services.httpserver.server.Client.handle(Client.java:92)

at com.sap.engine.services.httpserver.server.Processor.request(Processor.java:147)

at com.sap.engine.core.service630.context.cluster.session.ApplicationSessionMessageListener.process(ApplicationSessionMessageListener.java:37)

at com.sap.engine.core.cluster.impl6.session.UnorderedChannel$MessageRunner.run(UnorderedChannel.java:71)

at com.sap.engine.core.thread.impl3.ActionObject.run(ActionObject.java:37)

at java.security.AccessController.doPrivileged(Native Method)

at com.sap.engine.core.thread.impl3.SingleThread.execute(SingleThread.java:94)

at com.sap.engine.core.thread.impl3.SingleThread.run(SingleThread.java:162)

Thanks in advance

Subra