OWA or ECP stops working after installing EXCHANGE security update (SU) or HOT FIX update (HU) KBxxxxxx

SYMPTOMS

ECP displays the following error message:

Server Error in ‘/ecp’ Application.
Could not load file or assembly ‘Microsoft.Exchange.Common, Version=15.0.0.0 …Culture=neutral, PublicKeyToken=31bf3856ad364e54’ or one of its dependencies. The system cannot find the file specified.

OPTION 1:

1. Copy the Exchange KB to C:\Temp
2. Open COMMAND PROMPT as administrator
3. Type the full path of the .msp file (e.g. C:\temp\kbxxxxxxx.msp) , and then press Enter.
4. After the update installs, restart the server.

After restart, Check whether you can now access OWA and ECP on the server without getting an error message.

If the ECP error message continues to display, do the following:

1. Start IIS Manager on the server.
   
   
2. Navigate to Exchange Backend website > ECP Virtual directory.
   
   
3. Select Application settings > BinsearchFolder.
   
   
4. Check the paths to the Exchange directories that are listed. You might see directory paths that resemble the following:

%ExchangeInstallDir%bin;
%ExchangeInstallDir%bin\CmdletExtensionAgents;
%ExchangeInstallDir%ClientAccess\Owa\bin

5. Replace the paths with the following paths:

E:\Exchange ServerV15\bin;
E:\Exchange ServerV15\bin\CmdletExtensionAgents;
E:\Exchange ServerV15\ClientAccess\Owa\bin

Note The paths must point to where Exchange Server is installed on ACGV3, which is E Drive. Double check the paths above.

6. Start Exchange Management Shell as an administrator
7. Change directory to E:\Exchange ServerV15\bin  and run the following scripts: 

.\UpdateCas.ps1  (Takes a few min)

.\UpdateConfigFiles.ps1

8. Exit Exchange Management Shell and open a Command Prompt window as an administrator.
   
   
9. Run iisreset.exe
   
   
10. Restart the Exchange server
    
    
11. verify that you no longer get an error message when you access ECP.