ASP.NET 2.0, Trouble again

Event:
aspnet_wp.exe  (PID: 2128) stopped unexpectedly.

Failed to execute the request because the ASP.NET process identity does not have read permissions to the global assembly cache. Error: 0x80131902 

Failed to initialize the AppDomain:/LM/W3SVC/8/Root

Exception: System.Configuration.ConfigurationErrorsException
Message: Exception of type 'System.Configuration.ConfigurationErrorsException' was thrown.
StackTrace:    at System.Web.Configuration.ErrorRuntimeConfig.ErrorConfigRecord.System.Configuration.Internal.IInternalConfigRecord.GetLkgSection(String configKey)
   at System.Web.Configuration.RuntimeConfigLKG.GetSectionObject(String sectionName)
   at System.Web.Configuration.RuntimeConfig.GetSection(String sectionName, Type type, ResultsIndex index)
   at System.Web.Configuration.RuntimeConfig.get_HostingEnvironment()
   at System.Web.Hosting.HostingEnvironment.StartMonitoringForIdleTimeout()
   at System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters)
   at System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters)
   at System.Web.Hosting.ApplicationManager.CreateAppDomainWithHostingEnvironment(String appId, IApplicationHost appHost, HostingEnvironmentParameters hostingParameters)
   at System.Web.Hosting.ApplicationManager.CreateAppDomainWithHostingEnvironmentAndReportErrors(String appId, IApplicationHost appHost, HostingEnvironmentParameters hostingParameters)

今天再一次被ASP.NET迷惑了。
服务器是Win2kServer，已经装有.net framework1.1.4322并运行正常，目前装上.net framework2.0.50727，运行时产生Server Application Unavailable错误。The web application you are attempting to access on this web server is currently unavailable.Please hit the "Refresh" button in your web browser to retry your request.真是搞不懂了。