How to fix problem with ISAPI filters
Sometimes, after a Parallels Plesk Panel (Plesk) upgrade procedure, the Plesk Control Panel or client sites do not work correctly due to problems with third-party or Plesk ISAPI filters.
You may see an HTTP Error 500 while browsing a website or using Plesk on Windows.
The following error is shown when attempting to open a site within the server:
HTTP Error 500.0 - Internal Server Error Calling LoadLibraryEx on ISAPI filter "C:\Parallels\Plesk\isapi\isapirewrite4.dll" failed
You may also see the following error message:
Failed to run command 'cmd /C ""C:\Program Files (x86)\Parallels\Plesk\bin\ipmanage.exe" --xml-info"' Exit code: 1
ISAPI filters can be global, for all IIS sites or local sites, or for specific IIS sites.
You can check the installed global ISAPI filters in the Internet Information Server (IIS) Manager:
Then, check the file that the existing ISAPI filter refers to:
Users psacln and psaadm have no explicit prohibition (deny) for reading and execution of this file:
For the Plesk Control Panel site, separate ISAPI filters should be installed. A “Rewrite” filter should be installed as a minimum, with reference to the
"%plesk_dir%\isapi\isapirewrite4.dll" file. All files to which the Plesk ISAPI filters refer should include reading and executing rights for the users psacln and psaadm, and NETWORK SERVICE should be explicitly installed: