Exchange 2016 - Issues with ECP/OWA after installing updates/KB

For several reasons after installation updates/KB (for example KB4536987) you may faced with some backfires. I collected 3 type of issues and their fixes.

Issue #1 - Lack os styles on ECP page

After authentication on ECP page you may see only text and hyperlinks without any images and styles.

How to fix

Run the script "C:\Program Files\Microsoft\Exchange Server\V15\Bin\UpdateCas.ps1" or do following manual steps:

• Go to "C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\ecp" folder and find the folder with latest version number of your server (e.g. "15.1.1913.7") and it will be empty.
• Open folder with previous version number (e.g. "15.1.1913.5") and copy all data to the new folder (e.g. "15.1.1913.7").
• Restart IIS. Reload the ECP page.

Issue #2 - Something went wrong with OWA

After authentication on OWA page you may get an error "Something went wrong".

How to fix

Run the script "C:\Program Files\Microsoft\Exchange Server\V15\Bin\UpdateCas.ps1" or do following manual steps:

• Go to "C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Owa\prem\" folder and find the folder with latest version number of your server (e.g. "15.1.1913.7") and it will be empty.
• Open folder with previous version number (e.g. "15.1.1913.5") and copy all data to the new folder (e.g. "15.1.1913.7").
• Restart IIS. Reload the OWA page.

Issue #3 - Server Error in '/ecp' Application

After authentication on ECP page you may get an error "Could not load file or assembly 'Microsoft.Exchange.Common, Version=15.0.0.0, Culture=neutral, PublicKeyToken=***' or one of its dependencies. The system cannot find the file specified.".

How to fix

• Check the value of "BinSearchFolders" variable in "Exchange Back End - ECP" application settings. If the value is "%ExchangeInstallDir%" change it to "C:\Program Files\Microsoft\Exchange Server\V15\bin;C:\Program Files\Microsoft\Exchange Server\V15\bin\CmdletExtensionAgents;C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Owa\bin".
• Restart IIS. Reload the ECP page.

How to avoid all of those issues

• Run the security update at an elevated command prompt.
• Before run the update stop all Microsoft Exchange services and set startup type to manual.