Server 2008 üzerinde iis7 kullanıyorsanız yada sitelerinizi Plesk 9. Plesk 9.5 Plesk 10 yardımı ile yönetiyorsanız aşağıdaki hata ile karşılaşmış olabilirsiniz. Ben yaklaşık bir gün boyunca sorunun çözümü ile uğraştım farklı çözüm önerileri var hiç birinden sonuç alamadım.çözüm yolu aşağıdaki gibidir.

Çözüm Yolu

Öncelikli olarak  %plesk_dir%etcDiskSecurity yolundaki disksecurity.xml dosyasını notepad ile açıyoruz. 
Sonra dosyanın içine 
<Entry AccounType="1" Account="Psacln" Path="C:Windowsassembly"  AceFlags="FilesOnly" AccessMask="Read" EntryFlags="0x0" /> 
satırını ekleyerek kayıt ediyoruz. Kayıt işlemi tamamlandıktan sonra başlattan çalıştır alanınıa gelerek 
"%plesk_bin%applysecurity" --apply komutunu çalıştırıyoruz. Bu işlem sunucu yoğunluğuna göre bir kaç dakika 
alabilir. Komut tamamlandıktan sonra IIS 7. yi restart etmemiz gerekmektedir.

Bu aşamadan sonra Asp.net siteleriniz hatasız çalışacaktır.

Hata mesajı

[UnauthorizedAccessException: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))]

[FileLoadException: Could not load file or assembly 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. Access is denied.]
   System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) +0
   System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) +43
   System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +127
   System.Reflection.Assembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +142
   System.Reflection.Assembly.Load(String assemblyString) +28
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +46

[ConfigurationErrorsException: Could not load file or assembly 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. Access is denied.]
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +613
   System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +57
   System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +178
   System.Web.Compilation.BuildProvidersCompiler..ctor(VirtualPath configPath, Boolean supportLocalization, String outputAssemblyName) +54
   System.Web.Compilation.CodeDirectoryCompiler.GetCodeDirectoryAssembly(VirtualPath virtualDir, CodeDirectoryType dirType, String assemblyName, StringSet excludedSubdirectories, Boolean isDirectoryAllowed) +600
   System.Web.Compilation.BuildManager.CompileCodeDirectory(VirtualPath virtualDir, CodeDirectoryType dirType, String assemblyName, StringSet excludedSubdirectories) +125
   System.Web.Compilation.BuildManager.CompileCodeDirectories() +265
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +320

[HttpException (0x80004005): Could not load file or assembly 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. Access is denied.]
   System.Web.Compilation.BuildManager.ReportTopLevelCompilationException() +58
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +512
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters) +729

[HttpException (0x80004005): Could not load file or assembly 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. Access is denied.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +8897659
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +85
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +333