Hi guys. Im an absolute EpiServer newbie. I'm struggling to upgrade an EpiServer site from 6.0 R2 to 7. I follow this guidance http://joelabrahamsson.com/upgrading-a-site-from-episerver-cms-6-to-episerver-7/. After fixing all the compiling errors i finally can build the solution successfully. But when i start the site i got the error

Method not found: 'Boolean EPiServer.DataAbstraction.PageType.op_Equality(EPiServer.DataAbstraction.PageType, EPiServer.DataAbstraction.PageType)'.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.MissingMethodException: Method not found: 'Boolean EPiServer.DataAbstraction.PageType.op_Equality(EPiServer.DataAbstraction.PageType, EPiServer.DataAbstraction.PageType)'.

Source Error:

Line 18:     {
Line 19: 
Line 20:         public Global()
Line 21:         {
Line 22:             base.PostAcquireRequestState += Application_PostAcquireRequestState;

Source File: D:\IT\Projects\EpiServer\xcenda-solution\xcenda-episerver-solution\xcenda-internet\global.asax.cs    Line: 20

Stack Trace:

[MissingMethodException: Method not found: 'Boolean EPiServer.DataAbstraction.PageType.op_Equality(EPiServer.DataAbstraction.PageType, EPiServer.DataAbstraction.PageType)'.]
   PageTypeBuilder.Abstractions.PageTypeRepository.Load(Guid guid) +0
   PageTypeBuilder.Synchronization.PageTypeLocator.GetExistingPageType(PageTypeDefinition definition) +161
   PageTypeBuilder.Synchronization.PageTypeSynchronizer.b__0(PageTypeDefinition definition) +23
   System.Linq.WhereListIterator`1.MoveNext() +78
   PageTypeBuilder.Synchronization.PageTypeSynchronizer.CreateNonExistingPageTypes(IEnumerable`1 pageTypeDefinitions) +74
   PageTypeBuilder.Synchronization.PageTypeSynchronizer.SynchronizePageTypes() +124
   PageTypeBuilder.Initializer.Initialize(InitializationEngine context) +193
   EPiServer.Framework.Initialization.ModuleNode.Execute(Action a, String key) +56
   EPiServer.Framework.Initialization.InitializationEngine.InitializeModules() +618
   EPiServer.Framework.Initialization.InitializationEngine.Initialize(HostType hostType) +161
   EPiServer.Framework.Initialization.InitializationModule.Initialize(HostType hostType) +419
   EPiServer.Framework.Initialization.InitializationModule.FrameworkInitialization(HostType hostType) +103
   EPiServer.Global..ctor() +108
   Xcenda.Global..ctor() in D:\IT\Projects\EpiServer\xcenda-solution\xcenda-episerver-solution\xcenda-internet\global.asax.cs:20
   ASP.global_asax..ctor() in c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\1a0fb349\a8c3dba7\App_global.asax.0.cs:0

[TargetInvocationException: Exception has been thrown by the target of an invocation.]
   System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0
   System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark) +138
   System.Activator.CreateInstance(Type type, Boolean nonPublic) +105
   System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, StackCrawlMark& stackMark) +1499
   System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes) +191
   System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture) +27
   System.Web.HttpRuntime.CreateNonPublicInstance(Type type, Object[] args) +82
   System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +300
   System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +343

[HttpException (0x80004005): Exception has been thrown by the target of an invocation.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +539
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +125
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +731

I suspect there are some problems with dlls version. Can anyone give me a easy-way suggestion or step-by-step guide because im very new to Episerver? Comments are appreciate. Thanks!