After upgrading Exchange server to the latest patch or CU, we found the error page after login to ECP or OWA. OWA will be showing a login screen that says ‘bad request’ after entering credentials and ECP will be showing “Could not load file or assembly ‘Microsoft.Exchange.Common, Version=188.8.131.52 …”
1. Open IIS Manager. Expand Sites > Exchange Back End.
2. Click ecp. Open Application Settings in /ecp Home.
3. Please check whether the value for “BinSearchFolders” is changed to an invalid value. For example, if your exchange file installation is on default location, please 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
4. Please run the IISRESET in CMD start as Administrator to restart the IIS.
5. Navigate to “C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\ecp.” Then backup the web.config and web.config.bak file. Then delete the web.config file and rename the “web.config.bak” to “web.config”. Then please run the IISRESET in CMD start as Administrator to restart the IIS.
6. Navigate to “C:\Program Files\Microsoft\Exchange Server\V15\Bin”, then run the UpdateCas.ps1 in this file to reset the ECP