Exchange 2016 OWA HTTP ERROR 500

Accessing Exchange Server 2019 /OWA and /ECP throws the errors: “Status code: 500” and “Could not load file or assembly ‘Microsoft.Exchange.Common, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ or one of its dependencies.”

Problem

You’ve noticed that after patching Exchange Server 2019 servers (for this example, the patch for HAFNIUM was applied), access to /OWA and /ECP now displays the following errors:

OWA

🙁

Something went wrong

Your request couldn’t be completed. HTTP Status code: 500.

X-ClientId: F8E662D41996402E8660EEEB0976EA50

request-id a5077939-13bd-4032-9471-d6c8dc221d5a

X-OWA-Error System.Web.HttpUnhandledException

X-OWA-Version 15.2.721.13

X-FEServer Exch01

X-BEServer Exch02

Date:3/8/2021 12:31:53 PM

InnerException: System.IO.DirectoryNotFoundException

Fewer details…

Refresh the page

ECP

Server Error in ‘/ecp’ Application.

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Could not load file or assembly ‘Microsoft.Exchange.Common, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ 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.Common, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ 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.Common, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ 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.Common, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ 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) +96

System.Type.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) +65

System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) +62

System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) +50

[ConfigurationErrorsException: Could not load file or assembly ‘Microsoft.Exchange.Common, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ 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) +572

System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, Boolean checkAptcaBit) +31

System.Web.Configuration.Common.ModulesEntry.SecureGetType(String typeName, String propertyName, ConfigurationElement configElement) +59

System.Web.Configuration.Common.ModulesEntry..ctor(String name, String typeName, String propertyName, ConfigurationElement configElement) +59

System.Web.HttpApplication.BuildIntegratedModuleCollection(List`1 moduleList) +221

System.Web.HttpApplication.GetModuleCollection(IntPtr appContext) +1103

System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +122

System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +173

System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +255

System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +347

[HttpException (0x80004005): Could not load file or assembly ‘Microsoft.Exchange.Common, Version=15.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ or one of its dependencies. The system cannot find the file specified.]

System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +552

System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +122

System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +737

You’ve noticed that reviewing the BinSearchFolders application settings for ecp folder in the Exchange Back End website shows that the Value is configured with %ExchangeInstallDir%:

Changing this to the path without using the variable appears to fix the ECP page but not OWA:

Solution

One of the possible solutions to correct the issue is to use the UpdateCas.ps1 script located in the \Microsoft\Exchange Server\V15\Bin folder to rebuild the /OWA and /ECP directory: