Issue Error 500 on login

[scerecer]

Server operating system version

Windows Server 2022 Standard

Plesk version and microupdate number

PANEL-WIN_18.0.76

When I try to access localhost:8443 I get a 500 error and plesk repair doesn't work because it shows the error: status 255, the php.log shows the following:

thrown in C:\Program Files (x86)\Plesk\admin\plib\vendor\composer\autoload_real.php on line 45
[2026-03-04 22:17:01] PHP Warning: require(C:\Program Files (x86)\Plesk\admin\plib\vendor\composer/../react/promise/src/functions_include.php): Failed to open stream: No such file or directory in C:\Program Files (x86)\Plesk\admin\plib\vendor\composer\autoload_real.php on line 45
[2026-03-04 22:17:01] PHP Fatal error: Uncaught Error: Failed opening required 'C:\Program Files (x86)\Plesk\admin\plib\vendor\composer/../react/promise/src/functions_include.php' (include_path='C:\Program Files (x86)\Plesk\admin\plib\vendor/plesk/zf1/library;C:\Program Files (x86)\Plesk\admin\plib') in C:\Program Files (x86)\Plesk\admin\plib\vendor\composer\autoload_real.php:45
Stack trace:
#0 C:\Program Files (x86)\Plesk\admin\plib\vendor\composer\autoload_real.php(49): {closure:ComposerAutoloaderInitPlesk::getLoader():41}('ad155f8f1cf0d41...', 'C:\\Program File...')
#1 C:\Program Files (x86)\Plesk\admin\plib\vendor\autoload.php(22): ComposerAutoloaderInitPlesk::getLoader()
#2 C:\Program Files (x86)\Plesk\admin\plib\Loader.php(23): require_once('C:\\Program File...')
#3 C:\Program Files (x86)\Plesk\admin\plib\pm\Loader.php(19): Loader::registerAutoload(true)
#4 C:\Program Files (x86)\Plesk\admin\plib\sdk.php(4): pm_Loader::registerAutoload()
#5 {main}
thrown in C:\Program Files (x86)\Plesk\admin\plib\vendor\composer\autoload_real.php on line 45

Any idea for solution it?

 

[Sebahat.hadzhi]

Hi, @scerecer . The error usually indicates that an update was interrupted. Could you please connect to the server via RDP and execute the following command to continue the update:

plesk installer

 

[scerecer]

When I run the Plesk installer it does not allow me to update the version,

 

[scsa20]

You could try running

plesk repair installation

or download the Plesk Installer and run

plesk-installer.exe --console

And follow the instructions