We today noticed a bit of a problem on our Exchange 2013 CU2 server, or two actually:

1. After logging in to OWA the user just gets a blank page. If you check the source of that page it seems to be some sort of OWA loading script, but nothing shows up. This problem we can live with for now, but the second one is more critical:
2. After logging in to ECP the user only gets an IIS error page, displaying a stack trace.

Other services, such as ActiveSync and Outlook connectivity work just fine. OWA and ECP seem to have broken down rather unexpectedly as nothing has been changed/updated in the environment for a good while (honest to god!). KB2880833 was installed a month ago without any problems showing up at that time. These problems have appeared sometime later without any good explanation (no windows updates, no exhange updates, no nothing done on the server since KB2880833).

The server is an Exchange 2013 CU2 (with KB2880833) running on a Windows 2012 server. 

When googling around I can only find one related discussion, and the conclusion of that one is not convincing. 

Does anyone have any ideas about what to do to fix the below problem?

The error displayed when trying to access ECP reads:

Server Error in '/ecp' Application.

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Could not load file or assembly 'Microsoft.Exchange.Security' or one of its dependencies. The system cannot find the file specified.

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.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Exchange.Security' or one of its dependencies. The system cannot find the file specified.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Assembly Load Trace: The following information can be helpful to determine why the assembly 'Microsoft.Exchange.Security' could not be loaded.

WRN: Assembly binding logging is turned OFF. To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1. Note: There is some performance penalty associated with assembly bind failure logging. To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog].

Stack Trace:

[FileNotFoundException: Could not load file or assembly 'Microsoft.Exchange.Security' or one of its dependencies. The system cannot find the file specified.] System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMarkHandle stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName, ObjectHandleOnStack type) +0 System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName) +153 System.Type.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) +63 System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) +124 System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) +76 [ConfigurationErrorsException: Could not load file or assembly 'Microsoft.Exchange.Security' or one of its dependencies. The system cannot find the file specified.] System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) +12773840 System.Web.Configuration.Common.ModulesEntry.SecureGetType(String typeName, String propertyName, ConfigurationElement configElement) +69 System.Web.Configuration.Common.ModulesEntry..ctor(String name, String typeName, String propertyName, ConfigurationElement configElement) +66 System.Web.HttpApplication.BuildIntegratedModuleCollection(List`1 moduleList) +300 System.Web.HttpApplication.GetModuleCollection(IntPtr appContext) +1262 System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +133 System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +304 System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +404 System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +475 [HttpException (0x80004005): Could not load file or assembly 'Microsoft.Exchange.Security' or one of its dependencies. The system cannot find the file specified.] System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +12966756 System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +159 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +12806561

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Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.18408             

The following can be found in the Application Event logs:

- System 

  - Provider 

   [ Name]  ASP.NET 4.0.30319.0 
 
  - EventID 1310 

   [ Qualifiers]  32768 
 
   Level 3 
 
   Task 3 
 
   Keywords 0x80000000000000 
 
  - TimeCreated 

   [ SystemTime]  2014-01-14T19:29:59.000000000Z 
 
   EventRecordID 1050164 
 
   Channel Application 
 
   Computer HQ-MAIL01.contoso.local 
 
   Security 
 

- EventData 

   3008 
   A configuration error has occurred. 
   2014-01-14 20:29:59 
   2014-01-14 19:29:59 
   157875670aca4d23b9b08d362a1abd40 
   1 
   1 
   0 
   /LM/W3SVC/2/ROOT/ecp-11-130342013972690726 
   Full 
   /ecp 
   C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\ecp\ 
   HQ-MAIL01 
    
   7456 
   w3wp.exe 
   NT AUTHORITY\SYSTEM 
   ConfigurationErrorsException 
   Could not load file or assembly 'Microsoft.Exchange.Security' or one of its dependencies. The system cannot find the file specified. at System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) at System.Web.Configuration.Common.ModulesEntry.SecureGetType(String typeName, String propertyName, ConfigurationElement configElement) at System.Web.Configuration.Common.ModulesEntry..ctor(String name, String typeName, String propertyName, ConfigurationElement configElement) at System.Web.HttpApplication.BuildIntegratedModuleCollection(List`1 moduleList) at System.Web.HttpApplication.GetModuleCollection(IntPtr appContext) at System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) at System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) at System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) at System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) Could not load file or assembly 'Microsoft.Exchange.Security' or one of its dependencies. The system cannot find the file specified. at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMarkHandle stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName, ObjectHandleOnStack type) at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName) at System.Type.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) at System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) at System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase)  
   https://hq-mail01.contoso.local:444/ecp 
   /ecp 
   fe80::54dc:ab18:5381:d77b%19 
    
   False 
    
   NT AUTHORITY\SYSTEM 
   105 
   NT AUTHORITY\SYSTEM 
   False 
   at System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) at System.Web.Configuration.Common.ModulesEntry.SecureGetType(String typeName, String propertyName, ConfigurationElement configElement) at System.Web.Configuration.Common.ModulesEntry..ctor(String name, String typeName, String propertyName, ConfigurationElement configElement) at System.Web.HttpApplication.BuildIntegratedModuleCollection(List`1 moduleList) at System.Web.HttpApplication.GetModuleCollection(IntPtr appContext) at System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) at System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) at System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) at System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) 

Thanks!