How to fix problem with ISAPI filters

Symptoms

Sometimes, after a Plesk upgrade procedure, the Plesk or client sites do not work correctly due to problems with third-party or Plesk ISAPI filters.

The error HTTP Error 500 may be seen while browsing a website or using Plesk on Windows.

The following error is shown when attempting to open a site on the server:

PLESK_INFO: HTTP Error 500.0 - Internal Server Error Calling LoadLibraryEx on ISAPI filter "C:\\Parallels\\Plesk\\isapi\\isapirewrite4.dll" failed

OR

PLESK_INFO: Failed to run command 'cmd /C ""C:\\Program Files (x86)\\Parallels\\Plesk\\bin\\ipmanage.exe" --xml-info"' Exit code: 1

Resolution

ISAPI filters can be global, for all IIS sites or local sites, or for specific IIS sites.

Connect to the server using RDP and 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 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: