Symptoms

When loading Plesk the following error is displayed:

HTTP Error 503. The service is unavailable

In Event Viewer > Windows Logs > Application the following error:

The Module DLL C:\\Program Files (x86)\\iisnode\\iisnode.dll failed to load. The data is the error.

Cause

Plesk users psaadm and psacln do not have access to C:\\Program Files (x86)\\iisnode\\ directory by default.

Resolution

Perform the following steps to fix the issue:

1. Add the following lines into the disksecurity.xml file which is stored in %plesk_dir%\\etc\\DiskSecurity\\ directory:

   <!-- Program Files\\iisnode -->
   <Entry AccounType="1" Account="Psaadm" Path="{ProgramFiles}" SubPath="iisnode"     AceFlags="ThisFolderSubfoldersAndFiles" AccessMask="Read" EntryFlags="0x40" />
   <Entry AccounType="1" Account="Psacln" Path="{ProgramFiles}" SubPath="iisnode"     AceFlags="ThisFolderSubfoldersAndFiles" AccessMask="Read" EntryFlags="0x40" />
   

2. Run Plesk Reconfigurator to correct disk permissions or correct them manually:

   Go to `C:\\Program Files (x86)\\` and right-click on `iisnode`.
   In opened window click on **Security > psacln**.
   Assign read and access permissions for `psacln`.
   In IIS start stopped application pools.
   

3. Restart Plesk Management Service service.

If it does not solve the issue:

1. Back up IIS configuration file.

   copy "%windir%\\System32\\inetsrv\\config\\applicationHost.config" "%windir%\\System32\\inetsrv\\config\\applicationHost.config.bak"
   

2. Remove iisnode module under IIS > Sites > PleskControlPanel > Module .

Additional information

#2139415251 - Websites show 503 Service Unavailable error. In Event Viewer: iisnode.dll failed to load.