MWS Homepage is not accessible

Hi,
We are facing a weird issue with MWS.

MWS Process is available and logs shows MWS is initialized successfully but MWS login page is not displaying and we are getting below error, when trying to access the MWS URL.
Can anybody throw some light on this error please?
Thanks in advance.

Note: We haven’t installed any new fixes, no changes were done to MWS but suddenly we are facing this problem.

2013-02-11 21:30:17 GMT+08:00 (Framework : INFO) - My webMethods Server “default” Node “master” took 48 seconds to inititalize

2013-02-11 21:30:18 GMT+08:00 (Framework : FATAL) [RID:1] - com.webmethods.portal.mech.storage.impl.BasicMechanics incompatible with com.webmethods.portal.mech.themes.ISkinMechanics
java.lang.ClassCastException: com.webmethods.portal.mech.storage.impl.BasicMechanics incompatible with com.webmethods.portal.mech.themes.ISkinMechanics
at com.webmethods.portal.framework.presentation.PresentationManager.setSessionData(PresentationManager.java:532)
at com.webmethods.portal.framework.presentation.PresentationManager.preparePresentationData(PresentationManager.java:237)
at com.webmethods.portal.framework.dispatch.DispatchManager.preparePresentationData(DispatchManager.java:810)
at com.webmethods.portal.framework.dispatch.DispatchManager.handle(DispatchManager.java:432)
at com.webmethods.portal.framework.dispatch.DispatchManager.handleDispatch(DispatchManager.java:371)
at com.webmethods.portal.framework.impl.PortalServlet.service(PortalServlet.java:249)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:428)
at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:830)
at com.webmethods.portal.framework.impl.NTLMFilter.doFilter(NTLMFilter.java:66)
at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:821)
at com.webmethods.caf.faces.servlet.GZIPFilter.doFilter(GZIPFilter.java:36)
at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:821)
at com.webmethods.portal.framework.impl.RequestFilter.doFilter(RequestFilter.java:56)
at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:821)
at com.webmethods.caf.faces.servlet.XSSFilter.doFilter(XSSFilter.java:22)
at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:821)
at org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:471)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:568)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1530)
at org.mortbay.jetty.servlet.WebApplicationContext.handle(WebApplicationContext.java:633)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1482)
at com.webmethods.portal.webApplication.WmWebAppContext.handle(WmWebAppContext.java:161)
at org.mortbay.http.HttpServer.service(HttpServer.java:909)
at org.mortbay.http.HttpConnection.service(HttpConnection.java:820)
at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:986)
at org.mortbay.http.HttpConnection.handle(HttpConnection.java:837)
at org.mortbay.http.SocketListener.handleConnection(SocketListener.java:245)
at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:357)
at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:534)
2013-02-11 21:30:18 GMT+08:00 (org.mortbay.jetty.context.webMethods Portal : ERROR) - /:
java.lang.ClassCastException: com.webmethods.portal.mech.storage.impl.BasicMechanics incompatible with com.webmethods.portal.mech.themes.ISkinMechanics
at com.webmethods.portal.framework.presentation.PresentationManager.setSessionData(PresentationManager.java:532)
at com.webmethods.portal.framework.presentation.PresentationManager.preparePresentationData(PresentationManager.java:237)
at com.webmethods.portal.framework.dispatch.DispatchManager.preparePresentationData(DispatchManager.java:810)
at com.webmethods.portal.framework.dispatch.DispatchManager.handle(DispatchManager.java:432)
at com.webmethods.portal.framework.dispatch.DispatchManager.handleError(DispatchManager.java:405)
at com.webmethods.portal.framework.error.ErrorManager.handleException(ErrorManager.java:97)
at com.webmethods.portal.framework.impl.PortalServlet.service(PortalServlet.java:254)

Newly created MWS was pointed to the existing & working MWS DB, so it screwed up working MWS and threw above mentioned errors.
It forced us to restore MWS from tape backup :frowning: .