Plesk graphical interface (GUI) is not accessible: Call to a member function getAttribute() on a non-object (DefPackageMng.php:231)

Symptoms

• Plesk Obsidian running on a Windows Server
• One of the following errors is shown when logging into the Plesk GUI:

ERROR: Call to a member function getAttribute() on a non-object (DefPackageMng.php:231)

ERROR: Call to a member function getAttribute() on null (DefPackageMng.php:258)

Cause

The file %plesk_dir%\admin\db\defpackagemng.xml is either absent or corrupted. 

Resolution

1. Connect to the server via RDP
2. Move the file to another location (if it exists)
3. Run Command Prompt as the Windows Administrator
4. Execute the command below to regenerate the defpackagemng.xml file:

   C:\> "%plesk_bin%\defpackagemng.exe" --get --force