Error on Plesk for Windows server: Module "IsapiCachesModule" could not be found

Symptoms

• On a Plesk for Windows server, instead of the login page, users will see a blank screen with the title "500 Internal server error".

• The following error can now be seen instead of the blank screen after the steps below are executed:

  1. Edit C:\Program Files (x86)\Plesk\admin\htdocs\web.config and set errorMode="DetailedLocalOnly" then save the file.

  2. Open the Plesk login page again within the server browser.

     HTTP Error 500.0 - Internal Server Error
     Module "IsapiCachesModule" could not be found

• An antivirus has quarantined files from the C:\Windows\System32\inetsrv folder.

Cause

DLL system files were infected from an unknown source.

Resolution

Contact Microsoft Support to obtain a genuine copy of the missing files.