Type mismatch on load from second level cache - nhibernate

Question

I have a clustered web app running in asp.net + nhibernate that relies in MemcacheD as its second level cache provider. Everything ran fine for months and today some queries started to give a type mismatch error when loading entities from cache L2. Restarting the cache appeared to solve the problem, but a few minutes later the error returned. Right now the cache is disabled and everything is working.
Any clue is appreciated.
Stacktrace:
System.Web.HttpUnhandledException: Exception of type 'System.Web.HttpUnhandledException' was thrown.
---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
---> NHibernate.TypeMismatchException: Provided id of the wrong type. Expected: System.Int32, got System.Int64
at NHibernate.Event.Default.DefaultLoadEventListener.OnLoad(LoadEvent event, LoadType loadType)
at NHibernate.Impl.SessionImpl.FireLoad(LoadEvent event, LoadType loadType)
at NHibernate.Impl.SessionImpl.InternalLoad(String entityName, Object id, Boolean eager, Boolean isNullable)
at NHibernate.Type.EntityType.ResolveIdentifier(Object id, ISessionImplementor session)
at NHibernate.Type.TypeFactory.Assemble(Object[] row, ICacheAssembler[] types, ISessionImplementor session, Object owner)
at NHibernate.Cache.Entry.CacheEntry.Assemble(Object[] values, Object result, Object id, IEntityPersister persister, IInterceptor interceptor, ISessionImplementor session)
at NHibernate.Event.Default.DefaultLoadEventListener.AssembleCacheEntry(CacheEntry entry, Object id, IEntityPersister persister, LoadEvent event)
at NHibernate.Event.Default.DefaultLoadEventListener.LoadFromSecondLevelCache(LoadEvent event, IEntityPersister persister, LoadType options)
at NHibernate.Event.Default.DefaultLoadEventListener.DoLoad(LoadEvent event, IEntityPersister persister, EntityKey keyToLoad, LoadType options)
at NHibernate.Event.Default.DefaultLoadEventListener.Load(LoadEvent event, IEntityPersister persister, EntityKey keyToLoad, LoadType options)
at NHibernate.Event.Default.DefaultLoadEventListener.OnLoad(LoadEvent event, LoadType loadType)
at NHibernate.Impl.SessionImpl.FireLoad(LoadEvent event, LoadType loadType)
at NHibernate.Impl.SessionImpl.InternalLoad(String entityName, Object id, Boolean eager, Boolean isNullable)
at NHibernate.Type.EntityType.ResolveIdentifier(Object id, ISessionImplementor session)
at NHibernate.Engine.TwoPhaseLoad.InitializeEntity(Object entity, Boolean readOnly, ISessionImplementor session, PreLoadEvent preLoadEvent, PostLoadEvent postLoadEvent)
at NHibernate.Loader.Loader.InitializeEntitiesAndCollections(IList hydratedObjects, Object resultSetId, ISessionImplementor session, Boolean readOnly)
at NHibernate.Loader.Loader.DoQuery(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies)
at NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollections(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies)
at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters)
at NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes)
at NHibernate.Impl.SessionImpl.ListCustomQuery(ICustomQuery customQuery, QueryParameters queryParameters, IList results)
at NHibernate.Impl.SessionImpl.List(NativeSQLQuerySpecification spec, QueryParameters queryParameters, IList results)
at NHibernate.Impl.SessionImpl.List[T](NativeSQLQuerySpecification spec, QueryParameters queryParameters)
at NHibernate.Impl.SqlQueryImpl.List[T]() at Punchclock.DAL.NHibernate.UserDAO.GetUserList(QueryUser pQueryUser, Nullable`1 pTop)
at Punchclock.Biz.UserBiz.GetUserList(QueryUser queryUser, Nullable`1 pTop) at Punchclock.Biz.UserBiz.GetUserList(QueryUser queryUser, Int32 pTop)
at Punchclock.Net.Service.UserService.GetUserList(QueryUser queryUser, Int32 pTop)
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters) at Punchclock.Net.Service.ServiceProxy`1.Invoke(IMessage msg)
at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
at Punchclock.Core.Service.IUserService.GetUserList(QueryUser queryUser, Int32 pTop)
at Punchclock.Net.Delegate.UserDelegate.GetUserList(QueryUser queryUser, Int32 pTop)
at Punchclock.Client.Controller.UcUserQueryController.GetUserList(QueryUser queryUser, Int32 pTop)
at Punchclock.Client.Web.Record.UserControls.UcUserQuery.MakeQuery(Int32 maxResults)
at Punchclock.Client.Web.UserControls.UcQueryBase.OnQueryButtonClick(Object o, QueryEventArgs e)
at Punchclock.Client.Web.Record.UserControls.UcUserQuery.btnQuery_Click(Object sender, EventArgs e)
at System.Web.UI.WebControls.Button.OnClick(EventArgs e) at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument)
at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument)
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
--- End of inner exception stack trace ---
at System.Web.UI.Page.HandleError(Exception e)
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.UI.Page.ProcessRequest() at System.Web.UI.Page.ProcessRequest(HttpContext context)
at ASP.forms_query_aspx.ProcessRequest(HttpContext context)
in c:\WINDOWS\Microsoft.NET\Framework64\v2.0.50727\Temporary ASP.NET Files\punchclock_rc1\c4ca2e53\49a32ae2\App_Web_hfudjjsj.2.cs:line 0
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)